Faculty Profiles - AMANO, Hiroshi

15 GHz GaN Hi-Lo IMPATT Diodes With Pulsed Peak Power of 25.5 W Reviewed

Kawasaki, S; Kumabe, T; Deki, M; Watanabe, H; Tanaka, A; Honda, Y; Arai, M; Amano, H

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 71 ( 3 ) page： 1408 - 1415 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

The p+-n-n - n+ structure, known as Hi-Lo structure, was investigated in gallium nitride (GaN) single-drift-region (SDR) impact ionization avalanche transit-time (IMPATT) diodes to improve the output power and efficiency. The 15 GHz GaN Hi-Lo IMPATT diode was designed according to the Scharfetter and Gummel model under realistic conditions, suppressing the tunneling current (<10-4 cm2) and breakdown voltage (< 400 V). Even in such conditions, the calculated efficiency was higher than that of the p+-n abrupt junction structure and the improvement of RF characteristics was expected. The fabricated GaN Hi-Lo IMPATT diodes showed a clear avalanche breakdown and a pulsed microwave oscillation in the frequency range from 15 to 17 GHz. The maximum peak output power of 25.5 W and the efficiency of 2% were achieved, showing the highest values on microwave band GaN IMPATT diodes, and we confirmed that the Hi-Lo structure is effective for the high-power and high-efficiency operation of GaN IMPATT diodes.

DOI： 10.1109/TED.2023.3345822

Demonstration of AlGaN-on-AlN p-n Diodes With Dopant-Free Distributed Polarization Doping Reviewed Open Access

Kumabe T., Yoshikawa A., Kawasaki S., Kushimoto M., Honda Y., Arai M., Suda J., Amano H.

IEEE Transactions on Electron Devices 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

Nearly ideal vertical Al<inline-formula> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula>Ga<inline-formula> <tex-math notation="LaTeX">$_{\text{1}-\textit{x}}$</tex-math> </inline-formula>N (<inline-formula> <tex-math notation="LaTeX">$\text{0.7} \leq \textit{x} < \text{1.0}$</tex-math> </inline-formula>) p-n diodes are fabricated on an aluminum nitride (AlN) substrate. Distributed polarization doping (DPD) was employed for both p-type and n-type layers of the p-n junction, instead of conventional impurity doping, to overcome the major bottleneck of AlN-based material: the control of conductivity. Capacitance–voltage measurements revealed that the net charge concentration agreed well with the DPD charge concentration expected from the device layer structure. The fabricated devices exhibited a low turn-on voltage of 6.5 V, a low differential specific ON-resistance of 3 M<inline-formula> <tex-math notation="LaTeX">$\Omega$</tex-math> </inline-formula> cm<inline-formula> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula>, electroluminescence (maximum at 5.1 eV), and an ideality factor of 2 for a wide range of temperatures (room temperature—573 K). Moreover, the breakdown electric field was 7.3 MV cm<inline-formula> <tex-math notation="LaTeX">$^{-\text{1}}$</tex-math> </inline-formula>, which was almost twice as high as the reported critical electric field of GaN at the same doping concentration. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.

DOI： 10.1109/TED.2024.3367314

Junction Diameter Dependence of Oscillation Frequency of GaN IMPATT Diode Up to 21 GHz Reviewed

Kawasaki, S; Kumabe, T; Ando, Y; Deki, M; Watanabe, H; Tanaka, A; Honda, Y; Arai, M; Amano, H

IEEE ELECTRON DEVICE LETTERS Vol. 44 ( 8 ) page： 1328 - 1331 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Electron Device Letters

An experimental study on the effects of junction capacitance and current density on the oscillation characteristics of GaN single-drift-region (SDR) impact ionization avalanche transit-time (IMPATT) diodes were carried out using GaN p+-n abrupt junction diodes of various diameters, 200, 150, and 100 μ m , with a depletion layer width of 2 μ m. The fabricated diodes showed a clear avalanche breakdown at 315 V and a pulsed microwave oscillation with a peak output power exceeding 30 dBm. The oscillation frequency depended on junction diameter and current density. It was widely modulated from 8.56 to 21.1 GHz with decreasing junction diameter and increasing current density. The highest oscillation frequency was obtained with a current density of 13.8 kA/cm2 and a junction diameter of 100 μ m. A numerical calculation based on Read-type small-signal theory was carried out and found to well explain the experimental results.

DOI： 10.1109/LED.2023.3285938

Reverse Leakage Mechanism of Dislocation-Free GaN Vertical p-n Diodes Reviewed

Kwon, W; Kawasaki, S; Watanabe, H; Tanaka, A; Honda, Y; Ikeda, H; Iso, K; Amano, H

IEEE ELECTRON DEVICE LETTERS Vol. 44 ( 7 ) page： 1172 - 1175 2023.7

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Electron Device Letters

The reverse leakage mechanism of threading dislocation (TD)-free gallium nitride (GaN) vertical p-n diode was investigated in various temperature range, and it was compared with that of the p-n diode having a threading dislocation density (TDD) of around 10^6 cm -2. The reverse leakage current was increased markedly by increasing the temperature from 400 K, the dominant mechanism was explained by thermionic and Poole-Frenkel emissions for TD-free and high-TDD p-n diodes, respectively. At high temperatures and electric fields, the leakage current of the high TDD p-n diode showed 2 times higher than the TD-free p-n diode. These results indicate that the performance of vertical GaN devices, especially when employed at high temperatures and electric fields, can be enhanced by removing TDs.

DOI： 10.1109/LED.2023.3274306

Hole mobility limiting factors in dopant-free p-type distributed polarization-doped AlGaN Reviewed Open Access

Kumabe, T; Kawasaki, S; Watanabe, H; Honda, Y; Amano, H

APPLIED PHYSICS LETTERS Vol. 122 ( 25 ) 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We investigated the hole mobility limiting factors in dopant-free p-type distributed polarization-doped (DPD) AlGaN layers by an experimental method. p-DPD AlGaN exhibited a higher hole mobility than GaN:Mg with a similar room temperature hole concentration across all temperature ranges owing to the absence of ionized impurity scattering. In addition, unlike in n-DPD AlGaN, alloy scattering was not always critical in p-DPD AlGaN. The extracted alloy scattering potential was only 0.3 eV, which resulted in a reduced effect of alloy scattering and originated from a small valence band offset in the GaN/AlN heterojunction system. The results suggest that DPD principally enables the fabrication of low-resistance p-type nitride semiconductor thin films as a result of the high hole concentration and high hole mobility.

DOI： 10.1063/5.0155363

High In content nitride sub-micrometer platelet arrays for long wavelength optical applications Reviewed

Cai, WT; Furusawa, Y; Wang, J; Park, JH; Liao, YQ; Cheong, HJ; Nitta, S; Honda, Y; Pristovsek, M; Amano, H

APPLIED PHYSICS LETTERS Vol. 121 ( 21 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We demonstrate high, up to 30% In content InGaN sub-micrometer platelets on GaN by metalorganic vapor phase epitaxy. These InGaN platelets were selectively grown on flat GaN seeds formed in sub-micrometer-scale openings in a SiNx mask. The platelets were highly uniform without any dislocations or pits, with an atomically flat (0001) surface. The typical height was ∼120 nm, which significantly exceeded the normal critical layer thickness of a c-plane InGaN film. The strain state was comprehensively characterized by microbeam x-ray diffraction and transmission electron microscopy. Due to a gradual elastic relaxation of strain, the In content increased almost linearly from bottom to top because of the strong strain-dependent In incorporation. These platelets can serve as high-quality strain-relaxed templates for long wavelength micro-light-emitting diodes.

DOI： 10.1063/5.0120723

Tuning the p-type doping of GaN over three orders of magnitude via efficient Mg doping during halide vapor phase epitaxy Reviewed Open Access

Ohnishi, K; Fujimoto, N; Nitta, S; Watanabe, H; Lu, S; Deki, M; Honda, Y; Amano, H

JOURNAL OF APPLIED PHYSICS Vol. 132 ( 14 ) 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

The precise control of Mg concentration ([Mg]) in p-type GaN layers from 2.3 × 1016 to 2.0 × 1019 cm-3 was demonstrated by halide vapor phase epitaxy (HVPE) on n-type GaN (0001) freestanding substrates. [Mg] in GaN layers could be controlled well by varying the input partial pressure of MgCl2 formed by a chemical reaction between MgO solid and HCl gas under the thermodynamic equilibrium condition. In the sample with [Mg] of 2.0 × 1019 cm-3, a step-bunched surface was observed because the surface migration of Ga adatoms was enhanced by the surfactant effect of Mg atoms. The samples show high structural qualities determined from x-ray rocking curve measurements. The acceptor concentration was in good agreement with [Mg], indicating that almost all Mg atoms act as acceptors. The compensating donor concentrations in the samples were higher than the concentrations of Si, O, and C impurities. We also obtained the Mg acceptor level at a sufficiently low net acceptor concentration of 245 ± 2 meV. These results show that the HVPE method is promising for fabricating GaN vertical power devices, such as n-channel metal-oxide-semiconductor field-effect transistors.

DOI： 10.1063/5.0122292

Laser slice thinning of GaN-on-GaN high electron mobility transistors Reviewed Open Access

Tanaka, A; Sugiura, R; Kawaguchi, D; Wani, Y; Watanabe, H; Sena, H; Ando, Y; Honda, Y; Igasaki, Y; Wakejima, A; Ando, Y; Amano, H

SCIENTIFIC REPORTS Vol. 12 ( 1 ) page： 7363 2022.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

As a newly developed technique to slice GaN substrates, which are currently very expensive, with less loss, we previously reported a laser slicing technique in this journal. In the previous report, from the perspective of GaN substrate processing, we could only show that the GaN substrate could be sliced by a laser and that the sliced GaN substrate could be reused. In this study, we newly investigated the applicability of this method as a device fabrication process. We demonstrated the thinning of GaN-on-GaN high-electron-mobility transistors (HEMTs) using a laser slicing technique. Even when the HEMTs were thinned by laser slicing to a thickness of 50 mm after completing the fabrication process, no significant fracture was observed in these devices, and no adverse effects of laser-induced damage were observed on electrical characteristics. This means that the laser slicing process can be applied even after device fabrication. It can also be used as a completely new semiconductor process for fabricating thin devices with thicknesses on the order of 10 mm, while significantly reducing the consumption of GaN substrates.

DOI： 10.1038/s41598-022-10610-4

Continuous-wave lasing of AlGaN-based ultraviolet laser diode at 274.8 nm by current injection Reviewed Open Access

Zhang, ZY; Kushimoto, M; Yoshikawa, A; Aoto, K; Schowalter, LJ; Sasaoka, C; Amano, H

APPLIED PHYSICS EXPRESS Vol. 15 ( 4 ) 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

We demonstrated continuous-wave lasing of an AlGaN-based ultraviolet laser diode, fabricated on a single-crystal AlN substrate when operating at 5 °C. The threshold current density and device series resistance were reduced by improvements to the epitaxial structure and electrode arrangement. A peak wavelength of 274.8 nm was observed for lasing at a drive current over 110 mA, which corresponded to a threshold current density of 3.7 kA cm-2. The operating voltage at the threshold current was as low as 9.6 V.

DOI： 10.35848/1882-0786/ac6198

Ohmic contact on low-doping-density p-type GaN with nitrogen-annealed Mg Reviewed Open Access

Lu, S; Deki, M; Wang, J; Ohnishi, K; Ando, Y; Kumabe, T; Watanabe, H; Nitta, S; Honda, Y; Amano, H

APPLIED PHYSICS LETTERS Vol. 119 ( 24 ) 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We have demonstrated a fabrication process for the Ohmic contact on low-doping-density p-type GaN with nitrogen-annealed Mg. An Ohmic contact with a contact resistance of 0.158 ω cm2 is realized on p-GaN ([Mg] = 1.3 × 1017 cm-3). The contact resistance of p-type GaN with higher Mg concentration ([Mg]=1.0 × 1019 cm-3) can also be reduced to 2.8 × 10-5 ω cm2. A localized contact layer is realized without any etching or regrowth damage. The mechanism underlying this reduced contact resistance is studied by scanning transmission electron microscopy with energy dispersive x-ray spectroscopy and secondary ion mass spectrometry, representing a mutual diffusion of Ga and Mg atoms on the interface. Reductions in the barrier height and surface depletion width with the nitrogen-annealed Mg layer are confirmed by XPS and Hall effect measurements qualitatively.

DOI： 10.1063/5.0076764

Highly Oriented Epitaxial Hexagonal Boron Nitride Multilayers on High-Temperature-Resistant Single-Crystal Aluminum Nitride (0001).

Smart-cut-like laser slicing of GaN substrate using its own nitrogen Reviewed Open Access

Tanaka, A; Sugiura, R; Kawaguchi, D; Yui, T; Wani, Y; Aratani, T; Watanabe, H; Sena, H; Honda, Y; Igasaki, Y; Amano, H

SCIENTIFIC REPORTS Vol. 11 ( 1 ) page： 17949 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

We have investigated the possibility of applying lasers to slice GaN substrates. Using a sub-nanosecond laser with a wavelength of 532 nm, we succeeded in slicing GaN substrates. In the laser slicing method used in this study, there was almost no kerf loss, and the thickness of the layer damaged by laser slicing was about 40 µm. We demonstrated that a standard high quality homoepitaxial layer can be grown on the sliced surface after removing the damaged layer by polishing.

DOI： 10.1038/s41598-021-97159-w

Yang X, Pristovsek M, Nitta S, Honda Y, Ohtake A, Sakuma Y, Hiroto T, Ishida T, Ikezawa M, Guo Q, Amano H

Advanced science (Weinheim, Baden-Wurttemberg, Germany) page： e09354 2025.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Advanced Science

The epitaxy of high-quality hexagonal boron nitride (hBN) multilayers on dielectric wafers is essential for hBN applications but remains challenging. Herein, highly-oriented hBN multilayers grown on single-crystal aluminum nitride (AlN)—AlN on sapphire and bulk AlN substrates—via metalorganic vapor phase epitaxy and high-temperature annealing is reported. Hexagonal AlN (0001) not only provides a crystallographically commensurate base for hBN epitaxy but is thermally stable for hBN annealing up to 1800 °C, enabling the first instance of large-area multilayer hBN with both superior out-of-plane and in-plane alignments grown directly on dielectrics using a fully industry-compatible approach. Elevated temperatures also reduce carbon and allow control over the separation of related single photon emission centers in hBN. These centers exhibit a record-narrow wavelength distribution (578 ± 5 nm) with small zero-phonon linewidths down to 1.44 meV, indicating the high uniformity of the achieved multilayer hBN films. This work paves an industry-compatible way toward producing highly-oriented homogeneous hBN multilayers on dielectrics, promising for future device and integration applications.

DOI： 10.1002/advs.202509354

On barrier-free vertical GaN PN junction diode enabled by ion-implantation and ex-situ Mg diffusion process Open Access

Singh S., Kwon W., Li X., Wang J., Watanabe H., Honda Y., Amano H., Sarkar B.

Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers Vol. 64 ( 9 ) 2025.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers

This letter reports the application of ex-situ thermal diffusion of metallic Mg into GaN in mitigating the Schottky barrier that may arise underneath the standard Ni/Au contact to Mg ion-implanted GaN. The GaN PN junction diode realized after the Mg ion-implantation process resulted in a Schottky barrier in the p-side of the diode, in close agreement with the previous report. However, the diode that had an ex-situ thermal diffusion of Mg process after the ion-implantation process showed a dramatic increase in the forward current without introducing a compromise in the reverse breakdown voltage.

DOI： 10.35848/1347-4065/adfeef

SiN interlayer to improve external quantum efficiency and reduce sidewall recombination for blue (micro) light-emitting diodes

Pristovsek M., Park J.H., Kwon W., Cheong H., Amano H.

Applied Physics Letters Vol. 127 ( 7 ) 2025.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We demonstrate that inserting a fractional monolayer of SiN below the first InGaN quantum well (QW) does not change the In content but increases the external quantum efficiency (EQE) of light-emitting diodes (LEDs) and reduces the sidewall recombination, together with a small redshift and slight broadening of the emission. At low currents, we could directly measure the reduced emission from the sidewall of 80 μm diameter circular LEDs by inserting an SiN interlayer. This points to a reduced lateral diffusion of carriers in the QWs via an enhanced composition fluctuation indicated by the broadening of x-ray diffraction satellite peaks in addition to the formation of V-defects. Thus, the SiN interlayer increases the carrier localization in the QWs, which increases the EQE of LEDs due to fewer carriers reaching the sidewall as well as dislocations and point defects. The lateral localization of carriers could also explain the large scattering of the reported size dependencies of micro LEDs.

DOI： 10.1063/5.0272825

Advancements in ohmic contact technology for AlGaN/GaN high-electron-mobility transistors

Kim H.Y., Horng R.H., Amano H., Seong T.Y.

Progress in Quantum Electronics Vol. 102 2025.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Quantum Electronics

AlGaN/GaN-based high electron mobility transistors (HEMTs) hold significant technological importance due to their applications in power electronics, radio frequency (RF) amplifiers, and microwave communication systems. A critical factor affecting the performance of AlGaN/GaN HEMTs is the formation of high-quality ohmic contacts to the source and drain, which facilitates efficient carrier injection from metal electrodes to the semiconductor. Therefore, various approaches have been employed to achieve the formation of high-quality ohmic contacts. This review presents recent advancements in ohmic contact technology for AlGaN/GaN HEMTs. Specifically, we introduce and discuss contact technologies focusing on multilayer schemes under different annealing conditions, Au-free metallization schemes, surface treatments, non-traditional annealing processes, recess etching, selective area regrowth, and ion implantation.

DOI： 10.1016/j.pquantelec.2025.100578

Role of Sidewall Conditions in the External Quantum Efficiency of InGaN-Based Micro-LEDs Open Access

Park, JH; Pristovsek, M; Han, DP; Seong, TY; Amano, H

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS Vol. 19 ( 6 ) 2025.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi Rapid Research Letters

This study aims to investigate the external quantum efficiency (EQE) of InGaN-based blue micro light-emitting diodes (μLEDs) depending on sidewall conditions and current stress. To this end, this study prepares two sets of InGaN blue μLEDs with sizes of 10 × 10 μm2, 20 × 20 μm2, and 40 × 40 μm2: 1) μLEDs with and without a 10 nm-thick ALD-SiO<inf>2</inf> interlayer and 2) μLEDs with varying atomic layer deposition (ALD)-Al<inf>2</inf>O<inf>3</inf> passivation layer thickness and tetramethylammonium hydroxide (TMAH) treatment time. The results of set 1 demonstrate that the ALD-SiO<inf>2</inf> interlayer layer has a significant effect on the EQE of μLEDs only at low current densities, as the interlayer effectively protects against subsequent plasma damage. The results of current stress show that the ALD-SiO<inf>2</inf> interlayer plays an important role at low current densities. The results of set 2 demonstrate that a sufficiently thick ALD passivation layer should be deposited to minimize sidewall interface states, and a short TMAH treatment time of 1 min is sufficient. The results in this study highlight that sidewall conditions have a substantial impact on the EQE at low current densities and indicate that optimizing ALD thickness and TMAH treatment time can reduce processing time and cost.

DOI： 10.1002/pssr.202500042

Comparison of chip size effects of thin film GaN-based μLEDs fabricated by plasma etching and ion implantation processing Open Access

Wan T.C., Tsai P.H., Lin H.W., Lin C.C., Wuu D.S., Amano H., Seong T.Y., Horng R.H.

Applied Surface Science Advances Vol. 27 2025.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science Advances

We investigated the effects of chip size and N-polar n-GaN surface roughening on the performance of conventional thin-film blue-light micro-light-emitting diodes (TFFC μLEDs) and As+ ion isolated TFFC blue μLEDs. For this, TFFC μLEDs with two different sizes of 10 × 10 μm2 and 25 × 25 μm2 pixel array were fabricated. In all samples, N-face n-GaN surfaces were etched using a 4 M KOH solution after laser lift-off (LLO) process. A 2 min-etching resulted in the formation of pyramids (size: ∼90 – ∼270 nm), while the 4 min-etching produces pyramids (∼370 – ∼780 nm). Regardless of treatments, all samples exhibit similar forward bias characteristics. For all samples, the light output power increased after n-GaN surface roughening. Before the LLO process, the 10 μm-μLEDs showed higher EQE than the other samples with the implanted μLEDs showing the lowest EQE. All samples exhibited their highest EQE after optimal 4-min etching. Unlike before LLO, after 4 min-etching, the 10 μm- and 25 μm-μLEDs show almost similar EQEs, while the implanted μLEDs reveal a slightly lower EQE than the mesa μLEDs, but produce up to 74 % EQE improvement. Furthermore, the 10 μm-μLEDs showed the shortest photoluminescence (PL) decay, while the 25 μm-μLEDs gave the longest PL decay. The 10 μm μLEDs showed the highest ideality factor and the As+ ion-implanted μLEDs gave the lowest value. Based on time resolved PL and ideality factor, the size and etching time dependence of the EQE characteristics of all samples are described and discussed.

DOI： 10.1016/j.apsadv.2025.100776

Electron Spin Resonance and Photoluminescence Studies of Carbon-Induced Point Defects in GaN: Influence of Doping Concentration and Method Open Access

Honda, A; Watanabe, H; Kato, T; Honda, Y; Amano, H

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 2025.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi B Basic Research

The potential to modify the substitution of carbon (C) atom for gallium (Ga) or nitrogen (N) or the occupancy of the interstitial site for the different methods of C doping in gallium nitride is investigated. Herein, two types of samples with C doping concentrations of 1 × 1017, 1 × 1018, and 1 × 1019 cm−3 are prepared by supplying acetylene (C<inf>2</inf>H<inf>2</inf>) gas during growth and C autodoping. Based on the analysis of electron spin resonance and photoluminescence, it appears that the point defect generated by C substitution for the N site (C<inf>N</inf>) is formed in the C-doped sample with C<inf>2</inf>H<inf>2</inf> gas at C concentration of 1 × 1017 cm−3, and the defect changes to the C interstitial (C<inf>i</inf>) at C concentrations of 1 × 1018–1 ×1019 cm−3. In contrast, the C<inf>i</inf> defect is formed in the C autodoped samples at C concentrations of 1 × 1017–1 × 1018 cm−3 and changed to the C<inf>N</inf> defect at C concentration of 1 × 1019 cm−3. These results indicate the possibility that the formation mechanism of yellow luminescence band is different depending on the C doping method even at the same C concentration.

DOI： 10.1002/pssb.202500012

Characteristics of 2DEG generated at the heterointerface of an AlN/GaN structure grown on an AlN substrate using metal organic vapor phase epitaxy Open Access

Yoshikawa, A; Kumabe, T; Sugiyama, S; Arai, M; Suda, J; Amano, H

JOURNAL OF APPLIED PHYSICS Vol. 137 ( 19 ) 2025.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

A pseudomorphic AlN/GaN structure was grown on an AlN substrate using metalorganic vapor phase epitaxy (MOVPE). The Hall effect characteristics of two-dimensional electron gas induced at the interface between AlN and GaN and the properties of high-electron-mobility transistors (HEMTs) fabricated using the proposed AlN/GaN structures were investigated. The Hall effect measurements indicated that the electron mobility at room temperature was 294 cm2 V−1 s−1, the sheet carrier density was 1.1 × 1013 cm−2, and the sheet resistance was 1930 Ω/sq. Cross-sectional transmission electron microscopy images revealed an extremely abrupt interface between the AlN and GaN layers. By contrast, surface atomic force microscopy measurements indicated that GaN exhibited a clear step-terrace surface and the AlN barrier layer exhibited the signs of transitioning to island-like growth. Furthermore, the HEMT devices exhibited clear transistor characteristics with a source-drain breakdown voltage of 2.3 kV and an ON/OFF ratio of >107. These findings demonstrate the potential of MOVPE for fabricating AlN/GaN on AlN substrates, showing the inherent potential of AlN as a substrate.

DOI： 10.1063/5.0255068

Quantum efficiency characteristics of low-threading-dislocation-density InGaN photocathode grown on GaN substrate

Idei, M; Sato, D; Koizumi, A; Nishitani, T; Honda, Y; Amano, H

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Vol. 43 ( 3 ) 2025.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology B

The dependence of the quantum efficiency (QE) of a Cs/O-activated negative-electron-affinity (NEA) state InGaN photocathode on threading dislocation density (TDD) was investigated. InGaN photocathodes with different TDDs were grown on sapphire and GaN substrates by metal-organic vapor-phase epitaxy (MOVPE). The TDDs were 1 × 109 cm−2 on the sapphire substrate and less than 5 × 106 cm−2 on the GaN substrate. After the activation of the NEA state of InGaN photocathode surfaces by Cs/O, the QEs were 1.1% on the sapphire substrate and 0.91% on the GaN substrate. Despite a TDD difference of approximately two orders of magnitude, the QEs were comparable. The results show that the QE is not limited by the high TDD in the InGaN photocathode.

DOI： 10.1116/6.0004199

Modeling and Designing a GaN-Growth Reactor With Halogen-Free Vapor Phase Epitaxy: NH3 Decomposition at the Catalytic Surface of Components to Replicate Parasitic Polycrystal Formation Open Access

Shimazu, H; Nishizawa, SI; Nitta, S; Amano, H; Nakamura, D

IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING Vol. 38 ( 2 ) page： 311 - 323 2025.5

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Semiconductor Manufacturing

Achieving long-duration, large bulk GaN growth is crucial to supply low-cost, high-quality GaN. Halogen-free vapor phase epitaxy (HF-VPE) is a promising method for bulk GaN growth but faces challenges due to severe polycrystals deposition on reactor components, such as the source-gas nozzles, which impedes stable, extended growth. In this study, we developed models to simulate the polycrystal deposition in HF-VPE-GaN growth conditions by including surface reactions of GaN formation and NH3 decomposition. Moreover, we devised conditions for controlling gas flow and interdiffusion to suppress polycrystal deposition around the source-gas nozzles. Experimental results aligned with simulations, showing that increasing the distance between Ga and NH<inf>3</inf> nozzles and replacing the sheath gas from H<inf>2</inf> to N<inf>2 </inf>effectively minimized polycrystal formation. The findings confirm that reducing NH<inf>3</inf> concentration through catalytic surface decomposition on refractory components is crucial to polycrystal suppression. Optimizing nozzle dimensions and gas species synergistically controls the gas flow and interdiffusion. The constructed models contribute to advancing the design of polycrystal suppressive structures and conditions for long-duration bulk GaN growth.

DOI： 10.1109/TSM.2025.3558328

Understanding the Ga Polar n-GaN Surface after Mg Diffusion Process Open Access

Singh, S; Wang, J; Watanabe, H; Fregolent, M; De Santi, C; Meneghini, M; Badami, O; Asubar, JT; Amano, H; Sarkar, B

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 2025.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi A Applications and Materials Science

This work reports on the control of the n-GaN surface using a simple Mg diffusion process. It is shown that the Mg diffusion process enables a GaN surface without Fermi-level pinning. The process results in the realization of n-GaN unipolar camel diodes where increasing the metal work function leads to an incremental barrier height increase. Notably, the camel diode yields a record Schottky barrier height, indicating the possibility of improving the reverse characteristics of future GaN unipolar diodes.

DOI： 10.1002/pssa.202500090

All-GaN-Based Monolithic MIS-HEMT Integrated Micro-LED Pixels for Active-Matrix Displays Open Access

Furusawa, Y; Cai, WT; Cheong, HJ; Honda, Y; Amano, H

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 2025.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi A Applications and Materials Science

An all-GaN-based monolithic active-matrix micro-LED system that integrates metal-insulator-semiconductor high-electron-mobility transistors (MIS HEMTs) with light-emitting diodes (LEDs) is demonstrated. The proposed structure employs direct electron injection from the 2D electron gas (2DEG) in a HEMT, serving as the n-type layer, into the quantum wells of the LEDs. A 2-HEMT-1-LED pixel configuration is fabricated with one epitaxial growth, enabling the precise control of LED light output through a combination of select and drive HEMTs. The fabricated pixel achieved a maximum optical output density of 0.5 Wcm−2. A 2 × 2 pixel matrix is constructed with row and column lines connected via select HEMTs, demonstrating the capability of the 2-HEMT-1-LED pixel configuration for individual LED control.

DOI： 10.1002/pssa.202500044

Characterization of Quaternary AlxGa1-(x+y)InyN (x ≈ 0.5 and y ≤ 0.12) Metalorganic Vapor Phase Epitaxy Growth Focusing on Unintentionally Incorporated Impurities Open Access

Yamada, Y; Kumabe, T; Watanabe, H; Nitta, S; Honda, Y; Amano, H

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi B Basic Research

Quaternary AlGaInN has attracted attention because its physical properties such as bandgap, polarization, and lattice constant can be independently changed by controlling the AlN, GaN, and InN mole fractions. However, the complexity of crystal growth is problematic, and reducing unintentionally incorporated impurities that cause carrier scattering and compensation is crucial. In this study, about 30-nm-thick Al<inf>x</inf>Ga<inf>1−(x+y)</inf>In<inf>y</inf>N (x ≈ 0.5 and y ≤ 0.12) is grown on GaN on sapphire by metalorganic vapor phase epitaxy under various growth conditions to systematically analyze the relationship between growth conditions and oxygen and carbon concentrations ([O] and [C], respectively) as well as surface morphology and to elucidate the factors affecting [O] and [C]. [O] is decreased in samples grown at low growth rates and high growth temperatures. This can be attributed to the realization of a smooth surface morphology free of V-pits and trench defects. [C] is decreased in samples grown at a low total of group III source flow rates. The [C] of UID-GaN and that of AlGaInN at various TMI flow rates suggest that TMA mainly affects [C]. Therefore, the key to impurity reduction is to obtain a smooth surface morphology and to promote the adequate decomposition of TMA.

DOI： 10.1002/pssb.202500028

Vertical GaN p-n diode with deeply etched mesas by contactless photo-electrochemical etching Open Access

Toyoda, H; Kwon, W; Watanabe, H; Tsukamoto, R; Furusawa, Y; Itoh, Y; Honda, Y; Amano, H

APPLIED PHYSICS EXPRESS Vol. 18 ( 3 ) 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

GaN p-n diodes were fabricated by contactless photo-electrochemical (PEC) etching, and their electrical characteristics were evaluated. A high vertical etching rate of 80 nm min−1, which is usable for device fabrication etching processes, was achieved using a H₃PO₄ based electrolyte containing S₂O₈2⁻ ions and intense UV light. The sidewalls after etching were perpendicular to the substrate owing to the directivity of UV light. Vertical GaN p-n diodes with deeply etched mesas were fabricated by contactless PEC etching and avalanche breakdown was confirmed. The results point to an alternative method of fabricating high-performance GaN power devices.

DOI： 10.35848/1882-0786/adbc43

Normally-off AlGaN/GaN MIS-HEMTs with high 2DEG mobility enabled by shallow recess and oxygen plasma treatment Open Access

Ishiguro, M; Sekiyama, K; Baratov, A; Maeda, S; Igarashi, T; Tajuddin, NSBA; Islam, N; Terai, S; Yamamoto, A; Kuzuhara, M; Sarkar, B; Amano, H; Asubar, JT

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 64 ( 2 ) 2025.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

We demonstrate a normally-off operation in Al<inf>2</inf>O<inf>3</inf>/AlGaN/GaN MIS-HEMTs with a high two-dimensional electron gas (2DEG) mobility enabled by a shallow recess channel structure and oxygen plasma treatment. In the channel region, the original 25-nm-thick AlGaN barrier layer was thinned down to 9 nm, which in principle, should yield a normally-on operation. However, we show that a pre-insulator deposition oxygen plasma treatment shifts the threshold voltage to +1.4 V. The relatively thick AlGaN barrier facilitated a minimal sacrifice of channel 2DEG mobility retaining a value as high as 1800 cm2V−1s−1, resulting in a high drain current of 600 mA mm−1.

DOI： 10.35848/1347-4065/adb256

Fabrication of GaN vertical junction barrier Schottky diode by Mg diffusion from shallow N/Mg ion-implantation segment Open Access

Kwon, W; Itoh, Y; Tanaka, A; Watanabe, H; Honda, Y; Amano, H

APPLIED PHYSICS EXPRESS Vol. 18 ( 1 ) 2025.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

A vertical GaN p-n junction diode (PND) and junction barrier Schottky diode (JBSD) were fabricated by selective Mg diffusion. Mg was diffused from a shallow N/Mg ion-implantation segment to a depth of 800 nm with a concentration of 1 × 1017-3 × 1018 cm−3 by annealing with an AlN capping layer at 1300 ℃ for 5 min under atmospheric N<inf>2</inf> pressure. The PND and JBSD exhibited specific on-resistances of 2.3-2.6 mΩ cm2 and repeatable breakdowns at 1.95 kV without degradation in breakdown voltage or leakage current. Additionally, the JBSD achieved a high-on/off ratio of 9.1 × 107 between 1.5 V and −1 kV.

DOI： 10.35848/1882-0786/ada71a

High-speed modulation of probe current using scanning electron microscope with photocathode technology

Nishitani T., Sato D., Arakawa Y., Niimi K., Yasuda M., Koizumi A., Iijima H., Honda Y., Amano H.

Proceedings of SPIE the International Society for Optical Engineering Vol. 13426 2025

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE the International Society for Optical Engineering

Semiconductor inspection technology using e-beam-based voltage contrast (VC) observation provides information on the electrical state and characteristics of terminals with less than 100 nm size, such as the source, drain, and gate in a MOSFET. In VC observation, a nanometer-sized electron beam causes charge accumulation in the target electrode, which is detected as bright or dark according to its electrical state and characteristics. For reproducibility of VC observations for semiconductor inspection, it is essential to release the charge accumulation due to electron beam irradiation of the terminal via leakage currents around the terminal surface. For VC observation of target terminals in the field of view in SEM imaging, electron irradiation time can be used for charge accumulation and unirradiated time for release of charge accumulation within the electron beam scanning. Therefore, it is possible to repeatedly observe VC changes by appropriate selection of the irradiated electron beam current and scanning speed, in addition to the selection of the electron energy. In addition, more fine modulation of the irradiated electron beam current is essential to obtain VC observations with a higher dynamic range, but such modulation should not result in changes in the position or image quality of the SEM image. In this study, an SEM equipped with a photocathode electron gun (PC-SEM) was used to investigate the effect of beam current modulation by photoemission on the SEM image quality of position and focus. Furthermore, in VC observations integrating the local beam current modulation technology of the PC-SEM, the irradiation current was modulated only for the gate plugs in an nMOSFET, and changes in the contrast of the drain plugs were investigated.

DOI： 10.1117/12.3050433

On-State Current Increasing Structure of Source-Connected Polarization Superjunction Transistor Open Access

Kokubo E., Watanabe H., Deki M., Tanaka A., Nitta S., Honda Y., Amano H.

Physica Status Solidi A Applications and Materials Science 2025

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi A Applications and Materials Science

A structure is proposed for increasing the on-state current in a polarization superjunction (PSJ) field effect transistor (FET) using gallium nitride (GaN). A PSJ FET can achieve a high breakdown voltage, but in the simplest PSJ FET structure, the PSJ structure and the gate are integrated, so the input capacitance will increase, which is disadvantageous for high-speed switching. Therefore, a structure in which the PSJ structure is connected to the source electrode has been proposed. By connecting the PSJ structure to the source, the capacitance of the PSJ structure is on the output side, where it has little effect on switching. However, those structures suffer from reduced on-state current. To address this issue, a structure is investigated that increases the on-state current because the PSJ structure is etched into a comb shape, and a current path in the on-state is provided separately from the PSJ structure. It is confirmed that the on-state current can be improved by etching the PSJ region. The V<inf>BD</inf>·I<inf>D,sat</inf> product is calculated to evaluate the effectiveness of the comb-shaped PSJ structure. It is possible to improve the V<inf>BD</inf>·I<inf>D, sat</inf> product by 2.17 times compared to the PSJ FET without PSJ structure etching.

DOI： 10.1002/pssa.202500046

Technological Advancements in AlGaN-Based Deep Ultraviolet Laser Diodes

Kushimoto M., Zhang Z., Yoshikawa A., Aoto K., Honda Y., Sasaoka C., Amano H.

Cs Mantech 2025 2025 International Conference on Compound Semiconductor Manufacturing Technology 2025

Language：English Publishing type：Research paper (scientific journal) Publisher：Cs Mantech 2025 2025 International Conference on Compound Semiconductor Manufacturing Technology

AlGaN-based deep-ultraviolet (DUV) laser diodes (LDs) are expected to be applied to various applications such as sterilization, sensing, and laser processing as compact, efficient, and eco-friendly deep-ultraviolet light sources. To realize laser diodes operating in the DUV wavelength range (200 nm to 280 nm), our research group has achieved major breakthroughs such as high-quality AlGaN thin film crystals grown on AlN single-crystal substrates and p-type conductivity control through distributed polarization doping. As a result, pulsed lasing at room temperature was demonstrated. Furthermore, continuous-wave (CW) lasing has been successfully achieved by suppressing dislocation formation through stress concentration suppression and further design improvements. In this presentation, we will review the research results of our group on DUV LD devices and describe the key technologies that played an important role in these achievements.

Advances in Deep Ultraviolet Semiconductor Laser: From Material Challenges to Device Performance

Kushimoto M., Zhang Z., Yoshikawa A., Aoto K., Honda Y., Sasaoka C., Amano H.

2025 Conference on Lasers and Electro Optics Europe and European Quantum Electronics Conference CLEO Europe Eqec 2025 2025

Language：English Publishing type：Research paper (scientific journal) Publisher：2025 Conference on Lasers and Electro Optics Europe and European Quantum Electronics Conference CLEO Europe Eqec 2025

AlGaN-based deep ultraviolet (DUV) laser diodes (LDs) have garnered significant attention for a wide range of applications, including sterilization, sensing, and high-precision laser processing, owing to their compact size, high efficiency, and environmentally friendly properties. Despite these advantages, achieving practical device performance has been challenging due to the difficulty in realizing high-quality crystal growth and efficient carrier injection.

DOI： 10.1109/CLEO/EUROPE-EQEC65582.2025.11110927

Sn-doped n-type GaN freestanding layer: Thermodynamic study and fabrication by halide vapor phase epitaxy Reviewed Open Access

Ohnishi K., Hamasaki K., Nitta S., Fujimoto N., Watanabe H., Honda Y., Amano H.

Journal of Crystal Growth Vol. 648 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth

Results of a thermodynamic study of Sn doping and fabrication of a Sn-doped GaN freestanding layer with high structural quality by halide vapor phase epitaxy (HVPE) are described in this paper. Thermodynamic analysis revealed that SnCl2 and/or SnCl act as Sn precursors through the reaction between Sn metal and HCl gas. The equilibrium partial pressures of SnCl2 and SnCl increase with the input HCl partial pressure. To generate Sn precursors effectively, it is desirable that the reaction between Sn metal and HCl gas occurs in the inert gas ambient. On the basis of results of the thermodynamic study, the Sn-doped GaN freestanding layer with a Sn concentration of 5.7 × 1019 cm−3 is fabricated by removing the GaN seed substrate after HVPE growth. The Sn-doped GaN freestanding layer has high crystal quality, and the lattice constants along the c- and a-axes of the Sn-doped GaN freestanding layer are larger than those of the GaN seed substrate because of the high electron density and the size effect of Sn atoms.

DOI： 10.1016/j.jcrysgro.2024.127923

InGaN-based blue and red micro-LEDs: Impact of carrier localization

Park J.H., Pristovsek M., Han D.P., Kim B., Lee S.M., Hanser D., Parikh P., Cai W., Shim J.I., Lee D.S., Seong T.Y., Amano H.

Applied Physics Reviews Vol. 11 ( 4 ) 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Reviews

Herein, we investigate micro-light-emitting diodes (μLEDs) ranging in size from 160 × 160 to 10 × 10 μm2 and report that the differences in the behavior of InGaN-based blue (∼460 nm) and red (∼600 nm) μLEDs are related to carrier localization. The external quantum efficiency (EQE) of blue μLEDs decreases with size regardless of sidewall conditions, whereas that of red μLEDs is insignificant due to carrier localization. Atomic probe tomography examination of 30%, 15%, and 7.5% indium-concentrated InGaN layers used in red μLEDs shows that higher indium concentrations result in greater indium fluctuations, which promote carrier localization and thus shorten the diffusion length of carriers. Finally, by observing the peak wavelength of electroluminescence and the current density at peak EQE for both blue and red μLEDs, we find that radiative recombination rate in μLEDs is likely to be chip size dependent.

DOI： 10.1063/5.0195261

(Ultra)wide bandgap semiconductor heterostructures for electronics cooling

Cheng Z., Huang Z., Sun J., Wang J., Feng T., Ohnishi K., Liang J., Amano H., Huang R.

Applied Physics Reviews Vol. 11 ( 4 ) 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Reviews

The evolution of power and radiofrequency electronics enters a new era with (ultra)wide bandgap semiconductors such as GaN, SiC, and β-Ga2O3, driving significant advancements across various technologies. The elevated breakdown voltage and minimal on-resistance result in size-compact and energy-efficient devices. However, effective thermal management poses a critical challenge, particularly when pushing devices to operate at their electronic limits for maximum output power. To address these thermal hurdles, comprehensive studies into thermal conduction within semiconductor heterostructures are essential. This review offers a comprehensive overview of recent progress in (ultra)wide bandgap semiconductor heterostructures dedicated to electronics cooling and are structured into four sections. Part 1 summarizes the material growth and thermal properties of (ultra)wide bandgap semiconductor heterostructures. Part 2 discusses heterogeneous integration techniques and thermal boundary conductance (TBC) of the bonded interfaces. Part 3 focuses on the research of TBC, including the progress in thermal characterization, experimental and theoretical enhancement, and the fundamental understanding of TBC. Parts 4 shifts the focus to electronic devices, presenting research on the cooling effects of these heterostructures through simulations and experiments. Finally, this review also identifies objectives, challenges, and potential avenues for future research. It aims to drive progress in electronics cooling through novel materials development, innovative integration techniques, new device designs, and advanced thermal characterization. Addressing these challenges and fostering continued progress hold the promise of realizing high-performance, high output power, and highly reliable electronics operating at the electronic limits.

DOI： 10.1063/5.0185305

Growth and Characterization of High Internal Quantum Efficiency Semipolar (101̅3) GaN-Based Light Emitting Diodes

Hu N., Park J.H., Wang J., Amano H., Pristovsek M.

ACS Applied Electronic Materials Vol. 6 ( 11 ) page： 7960 - 7971 2024.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Electronic Materials

We report on the growth and characterization of semipolar (101̅3) InGaN/GaN light-emitting diodes (LEDs) on m-plane (101̅0) sapphire with high internal quantum efficiencies (IQEs). Based on earlier work on obtaining untwinned (101̅3) GaN templates on m-plane sapphire, we also succeeded in smoothing the relatively unstable (101̅3) surface using very low V/III ratios during metal-organic vapor phase epitaxy and in the growth of n-and p-doped layers to produce LEDs. Fitting the current-dependent emission, we found high IQEs, up to 86% at 460 nm. The IQEs decreased toward longer wavelengths, similar as for conventional Ga-polar (0001) oriented LEDs. However, the semipolar (101̅3) LEDs have their maximum IQE at much higher current densities than the polar (0001) LEDs due to the higher overlap between electron and hole wave function while maintaining a positive polarization. Together, this makes the (101̅3) orientation very attractive for future blue LEDs.

DOI： 10.1021/acsaelm.4c01312

Study on Degradation of Deep-Ultraviolet Laser Diode

窒化物半導体結晶の魅力と人・社会・地球への貢献 Open Access

天野浩

日本結晶学会誌 Vol. 66 ( Supplement ) page： s2 - s2 2024.11

Zhang, ZY; Yoshikawa, A; Kushimoto, M; Sasaoka, C; Amano, H

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 221 ( 21 ) 2024.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

The degradation of an AlGaN-based deep-ultraviolet laser diode during operation is studied. A rapid increase in threshold current without any facet mirror damage under direct current stress below the threshold current is observed, which is considered to limit the lifetime of continuous wave lasing to the level of seconds. The evolution of current–light and current–voltage characteristics suggests that the dominant mechanism of degradation is the increased loss of carriers before they can reach the active layer, i.e., the decrease in carrier injection efficiency. The decrease in emission intensity, which is more pronounced at lower current densities, and subsequent increase in sub-threshold current indicate the increase in defect density under current stress, which is similar to the well-analyzed degradation mechanism found in AlGaN-based light-emitting diodes.

DOI： 10.1002/pssa.202300946

Experimental study of gain characteristics in relation to quantum-well width of deep-ultraviolet laser diodes

Zhang Z., Kushimoto M., Yoshikawa A., Aoto K., Sasaoka C., Amano H.

Applied Physics Letters Vol. 125 ( 18 ) 2024.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

The gain characteristics of electrically injected AlGaN-based deep-ultraviolet laser diodes were studied with respect to their quantum-well (QW) width dependence by the analysis of the threshold currents and gains for various cavity lengths. Among the fabricated QWs with widths of d = 9, 4.5, and 3 nm, the QW with the smallest width of 3 nm was found to have the highest material gain and lowest transparency carrier density. In contrast to recent arguments in favor of wider QWs for deep-ultraviolet laser diodes, the strategy of narrowing QWs is still found to be effective in practical terms of reducing the threshold current density.

DOI： 10.1063/5.0240488

Discovering the incorporation limits for wurtzite AlP<inf>y</inf>N<inf>1−y</inf> grown on GaN by metalorganic vapor phase epitaxy Reviewed

Yang X., Furusawa Y., Kano E., Ikarashi N., Amano H., Pristovsek M.

Applied Physics Letters Vol. 125 ( 13 ) 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We report on the growth of AlPN on GaN/sapphire templates by metalorganic vapor phase epitaxy using tertiarybutylphosphine (tBP) and NH3 as group-V precursors. P is easy to incorporate into the group-III lattice site, forming PAl anti-site defects and shrinking lattice constants that are even beyond AlN since Al is larger than P. We found that higher temperatures favor P incorporation on the N-sublattice, forming AlPyN1−y, while growth temperatures below 1000 °C result in dominant P incorporation on the Al-sublattice, forming PAl anisites. Similarly, larger NH3 flows stabilize GaN, leading to flat interfaces, but favor the formation of PAl. Furthermore, the P incorporation into AlPyN1−y is non-linear. At very low tBP flows, it initially increases to reach a maximum. Further increasing the tBP flow increases mostly the incorporation of P on the Al-sublattice, and the c-lattice constant decreases again. This leaves a small window of low V/III ratios below 5 and low P/N ratios of 1% or smaller, leading up to ∼4% P incorporation at typical growth temperatures of GaN. However, at such low V/III ratios, GaN is not stable even with N2 carrier gas and requires optimized switching sequences to minimize its decomposition and preserve flat interfaces. Eventually, a 10 nm coherent layer of AlP0.01N0.99 could be reproducibly grown on top of GaN channels with a smooth surface, an abrupt AlPN/GaN interface, and a two-dimensional electron gas with an electron mobility of ∼675 cm2/V s and a sheet carrier density of 1.5 × 1013 cm−2 at room temperature.

DOI： 10.1063/5.0225115

Hole transport mechanism at high temperatures in p-GaN/AlGaN/GaN heterostructure Reviewed

Sikder, B; Hossain, T; Xie, QY; Niroula, J; Rajput, NS; Teo, KH; Amano, H; Palacios, T; Chowdhury, N

APPLIED PHYSICS LETTERS Vol. 124 ( 24 ) 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

This Letter reports an investigation of hole transport in p-GaN/AlGaN/GaN heterostructures through experimental and theoretical analyses under varied conditions. Highly non-linear current-voltage (I-V) characteristics, obtained via the linear transmission line method measurements, are utilized for this study. At low bias voltage, the transport can be ascribed to the Schottky nature of the contact, while at high bias, the conduction is observed to be governed by space-charge limited current (SCLC). The Schottky characteristics (Schottky barrier height and non-ideality factor) and the SCLC exponent were analyzed for devices with varying contact spacings and at different high temperatures. The SCLC exponent, m, is in the range of 2 ≤ m ≤ 4 depending on the applied voltage range, revealing the existence of the trap states in the channel region. The findings of this work indicate that the charge injection, field-induced ionization, and trap states in the p-GaN channel are critical factors in the current transport of p-GaN/AlGaN/GaN heterostructure.

DOI： 10.1063/5.0203344

Recent advances in micro-pixel light emitting diode technology Reviewed Open Access

Park, JH; Pristovsek, M; Amano, H; Seong, TY

APPLIED PHYSICS REVIEWS Vol. 11 ( 2 ) 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Reviews

Display technology has developed rapidly in recent years, with III-V system-based micro-light-emitting diodes (μLEDs) attracting attention as a means to overcome the physical limitations of current display systems related to their lifetime, brightness, contrast ratio, response time, and pixel size. However, for μLED displays to be successfully commercialized, their technical shortcomings need to be addressed. This review comprehensively discusses important issues associated with μLEDs, including the use of the ABC model for interpreting their behavior, size-dependent degradation mechanisms, methods for improving their efficiency, novel epitaxial structures, the development of red μLEDs, advanced transfer techniques for production, and the detection and repair of defects. Finally, industrial efforts to commercialize μLED displays are summarized. This review thus provides important insights into the potential realization of next-generation display systems based on μLEDs.

DOI： 10.1063/5.0177550

Impacts of vacancy complexes on the room-temperature photoluminescence lifetimes of state-of-the-art GaN substrates, epitaxial layers, and Mg-implanted layers Reviewed Open Access

Chichibu, SF; Shima, K; Uedono, A; Ishibashi, S; Iguchi, H; Narita, T; Kataoka, K; Tanaka, R; Takashima, S; Ueno, K; Edo, M; Watanabe, H; Tanaka, A; Honda, Y; Suda, J; Amano, H; Kachi, T; Nabatame, T; Irokawa, Y; Koide, Y

JOURNAL OF APPLIED PHYSICS Vol. 135 ( 18 ) 2024.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

For rooting the development of GaN-based optoelectronic devices, understanding the roles of midgap recombination centers (MGRCs), namely, nonradiative recombination centers and deep-state radiative recombination centers, on the carrier recombination dynamics is an essential task. By using the combination of time-resolved photoluminescence and positron annihilation spectroscopy (PAS) measurements, the origins of major MGRCs in the state-of-the-art GaN epilayers, bulk crystals, and Mg-implanted layers were identified, and their concentrations were quantified for deriving the capture coefficients of minority carriers. In this article, potential standardization of the room-temperature photoluminescence lifetime for the near-band-edge emission ( τ PL RT ) as the concentration of major MGRCs well below the detection limit of PAS is proposed. For n-GaN substrates and epilayers grown from the vapor phase, τ PL RT was limited by the concentration of carbon on N sites or divacancies comprising a Ga vacancy (VGa) and a N vacancy (VN), [VGaVN], when carbon concentration was higher or lower, respectively, than approximately 1016 cm−3. Here, carbon and VGaVN act as major deep-state radiative and nonradiative recombination centers, respectively, while major MGRCs in bulk GaN crystals were identified as VGa(VN)3 vacancy clusters in Na-flux GaN and VGa or VGaVN buried by a hydrogen and/or VGa decorated with oxygen on N sites, VGa(ON)3-4, in ammonothermal GaN. The values of τ PL RT in n-GaN samples are compared with those of p-GaN, in which τ PL RT was limited by the concentration of VGa(VN)2 in Mg-doped epilayers and by the concentrations of VGaVN and (VGaVN)3 in Mg-implanted GaN right after the implantation and after appropriate activation annealing, respectively.

DOI： 10.1063/5.0201931

Metastable atomic-ordered configurations for Al1/2Ga1/2N predicted by Monte-Carlo method based on first-principles calculations Reviewed Open Access

Gueriba, JS; Mizuseki, H; Cadatal-Raduban, M; Sarukura, N; Kawazoe, Y; Nagasawa, Y; Hirano, A; Amano, H

JOURNAL OF PHYSICS-CONDENSED MATTER Vol. 36 ( 13 ) 2024.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics Condensed Matter

Metastability of Aln/12Ga1−n/12N (n = 2–10: integer) with the 1–2 monolayer (ML) in-plane configuration towards the c [0001] direction has been demonstrated recently. To theoretically explain the existence of these metastable structures, relatively large calculation cells are needed. However, previous calculations were limited to the use of small calculation cell sizes to estimate the local potential depth (∆σ) of ordered Al1/2Ga1/2N models. In this work, we were able to evaluate large calculation cells based on the interaction energies between proximate Al atoms (δEAl–Al) in AlGaN alloys. To do this, δEAl–Al values were estimated by first-principles calculations (FPCs) using a (5a1 × 5a2 × 5c) cell. Next, a survey of the possible ordered configurations using various large calculation cell models was performed using the estimated δEAl–Al values and the Monte-Carlo method. Then, various ∆σ values were estimated by FPCs and compared with the configurations previously reported by other research groups. We found that the ordered configuration obtained from the (4a1 × 2a2 × 1c) calculation cell (C42) has the lowest ∆σ of −9.3 meV/cation and exhibited an in-plane configuration at the c(0001) plane having (–Al–Al–Ga–Ga–) and (–Al–Ga–) sequence arrangements observed along the m{11̄00} planes. Hence, we found consistencies between the morphology obtained from experiment and the shape of the primitive cell based on our numerical calculations.

DOI： 10.1088/1361-648X/ad1137

Investigation of carbon-related complexes in highly C-doped GaN grown by metalorganic vapor phase epitaxy Reviewed Open Access

Honda, A; Watanabe, H; Takeuchi, W; Honda, Y; Amano, H; Kato, T

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 63 ( 4 ) 2024.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

We investigated the C-related complexes in highly C-doped GaN by electron spin resonance (ESR) spectroscopy, Fourier transform IR spectroscopy (FTIR), and minority carrier transient spectroscopy (MCTS) measurements. In the ESR spectra, two resonances with g values of 2.02 and 2.04 were found to be assigned by (0/−) deep acceptor and (+/0) charge transition levels of carbon substituting for nitrogen site (CN). In the FTIR spectra, two local vibrational modes positioned at 1679 and 1718 cm−1 were confirmed to be associated with tri-carbon complexes of CN-CGa-CN (basal) and CN-CGa-CN (axial), respectively. In the MCTS spectra, we observed the hole trap level of E v + 0.25 ± 0.1 eV associated with the tri-carbon complexes, which are the dominant C-related defects, suggesting that these complexes affect the electronic properties in the highly C-doped GaN.

DOI： 10.35848/1347-4065/ad3b54

Improving the Barrier Height of N-Polar GaN Schottky Diodes Using Mg-Diffusion Process Reviewed

Sarkar, B; Wang, J; Watanabe, H; Amano, H

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 71 ( 3 ) page： 1416 - 1420 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

In this work, we report a low-cost methodology to increase the barrier height of N-polar GaN Schottky diodes. Physical vapor deposition (PVD) of Mg followed by a thermal diffusion anneal at 800 °C leads to the formation of N-polar GaN Camel diode offering a larger barrier height than the conventional N-polar GaN Schottky diodes. The increase in barrier height after the Mg diffusion process is validated using current-voltage ({I} - {V}) and capacitance-voltage (CV) measurements. A barrier height of 0.7 eV and a near-unity ideality factor observed in the N-polar GaN Camel diode confirms that the proposed Mg diffusion process is an alternative method for improving the performance of future N-polar GaN diodes.

DOI： 10.1109/TED.2023.3341831

Sn-doped n-type GaN layer with high electron density of 1020 cm-3 grown by halide vapor phase epitaxy Reviewed Open Access

Hamasaki, K; Ohnishi, K; Nitta, S; Fujimoto, N; Watanabe, H; Honda, Y; Amano, H

JOURNAL OF CRYSTAL GROWTH Vol. 628 2024.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth

A Sn-doped n-type GaN layer with a high electron density of 2 × 1020 cm−3 and a low resistivity of 8.7 × 10−4 Ω∙cm was grown by halide vapor phase epitaxy (HVPE). Sn doping was performed through the reaction between Sn metal and HCl gas. The Sn concentration markedly increased with decreasing growth temperature and the activation energy of Sn desorption from the GaN surface was found to be 4.1 eV. Smooth surfaces were obtained by introducing the Sn precursor even though the samples were grown at a low temperature of 905 °C, suggesting that Sn atoms act as surfactants and promote the migration of Ga adatoms. Almost all the Sn atoms act as donors in GaN below the Sn concentration of 2 × 1020 cm−3. These results indicate that using the Sn donor is promising for fabricating low-resistivity n-type GaN substrates by HVPE.

DOI： 10.1016/j.jcrysgro.2023.127529

Impacts of off-angle and off-direction on surface morphology of GaN grown by metalorganic vapor phase epitaxy on (0001) GaN substrate Reviewed

Watanabe, H; Nitta, S; Ando, Y; Ohnishi, K; Honda, Y; Amano, H

JOURNAL OF CRYSTAL GROWTH Vol. 628 2024.2

Impact of unintentionally formed compositionally graded layer on carrier injection efficiency in AlGaN-based deep-ultraviolet laser diodes Reviewed

Zhang Z., Yoshikawa A., Kushimoto M., Aoto K., Sasaoka C., Amano H.

Applied Physics Letters Vol. 124 ( 6 ) 2024.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Increasing the injection efficiency, a critical factor constraining the reduction in threshold current in AlGaN-based deep-ultraviolet laser diodes, represents one of the paramount remaining technical challenges. In this study, the impact of compositionally graded layers that were unintentionally formed at the interface between the p-cladding and the core layer on carrier injection efficiency was analyzed. Experimental evaluations using laser diodes have shown that the elimination of an unintentionally formed layer increases the injection efficiency above the threshold current, from the conventional 3% to 13%. It has been postulated that the electron overflow toward the p-side exerts a substantial deleterious effect on the injection efficiency. An improvement in this aspect is achieved by increasing the electron-blocking capability due to the improved interface abruptness between the p-cladding layer and the core layer. The lasing threshold was strongly reduced, and characteristic temperature increased from 76 to 107 K for the improved devices.

DOI： 10.1063/5.0184543

Optical activation of praseodymium ions implanted in gallium nitride after ultra-high pressure annealing Reviewed

Ito, S; Sato, S; Bockowski, M; Deki, M; Watanabe, H; Nitta, S; Honda, Y; Amano, H; Yoshida, K; Minagawa, H; Hagura, N

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 547 2024.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Lanthanide (Ln)-implanted gallium nitride (GaN) semiconductors have a variety of potential applications as light-emitting devices and quantum light sources, but their optical properties are not well understood. In this study, we investigate the room temperature optical properties of praseodymium (Pr) ion implanted single-crystal GaN and their changes upon ultrahigh pressure annealing (UHPA) up to 1480 °C. Photoluminescence (PL) spectra, luminescence transition lifetime, and excitation cross section of the implanted Pr ions are analyzed. In addition, the recovery of implantation-induced damage and the thermal diffusion of implanted Pr ions by UHPA are investigated by X-ray diffraction, Raman spectroscopy, and secondary ion mass spectrometry. The results show that the implantation damage is recovered by annealing at temperatures above 1200 °C, but Pr ions thermally diffuse to the surface as the annealing temperature increases. The annealing temperature at which a maximum PL intensity is obtained increases with increasing the implantation dose. However, the PL intensity decreases in all cases after annealing at 1480 °C, indicating that a quenching factor is dominant in this temperature range.

DOI： 10.1016/j.nimb.2023.165181

Impurity reduction in lightly doped n-type gallium nitride layer grown via halogen-free vapor-phase epitaxy Reviewed Open Access

Kimura, T; Shimazu, H; Kataoka, K; Itoh, K; Narita, T; Uedono, A; Tokuda, Y; Tanaka, D; Nitta, S; Amano, H; Nakamura, D

APPLIED PHYSICS LETTERS Vol. 124 ( 5 ) 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

The development of gallium nitride (GaN) vertical-type metal-oxide-semiconductor field-effect transistors and p-i-n diode devices has gathered increasing attention. These devices require an n-type drift layer with a low doping level of 1016 cm−3 or less, minimized point defects inhibiting electron conduction, and a layer approximately 10 μm thick. Therefore, a practical method with a growth rate of at least several tens of μm/h and impurity concentrations of less than 1015 cm−3, except for that of dopants, is necessary. Halogen-free vapor-phase epitaxy (HF-VPE) has a high growth rate suitable for fabricating thick drift layers and utilizes a simple reaction between Ga vapor and ammonia gas (without a corrosive halogen gas), resulting in lower impurity levels. Herein, we eliminated the quartz content from the high-temperature zone to reduce the excess unintentional Si doping and identified that the nitrile gloves used for the growth preparation are other impurity contamination sources. We obtained a lightly n-type ([Si]=∼1016 cm−3) GaN layer, in which C, O, B, Fe, Mg, Al, Ca, Cr, Zn, Ni, Mn, and Ti impurity contents were below the detection limits of secondary ion mass spectrometry. Deep-level transient spectroscopy revealed that electron traps at EC − 0.26 and at EC − 0.59 eV were 2.7 × 1013 and 5.2 × 1014 cm−3, respectively. Moreover, the Hall effect analysis showed the acceptor-type defect-compensating donor content as approximately 2.7 × 1015 cm−3, resulting in a high electron mobility of HF-VPE GaN in the 30-710 K temperature range. Furthermore, we identified the Ca impurity as a deep acceptor, another killer defect leading to mobility collapse.

DOI： 10.1063/5.0191774

Droop and light extraction of InGaN-based red micro-light-emitting diodes Reviewed

Park, JH; Pristovsek, M; Cai, WT; Kumabe, T; Choi, SY; Lee, DS; Seong, TY; Amano, H

SEMICONDUCTOR SCIENCE AND TECHNOLOGY Vol. 39 ( 1 ) 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Semiconductor Science and Technology

In this letter, we investigate the impact of periphery, width, length and area on the external quantum efficiency (EQE) of stripe-type InGaN-based red micro-light-emitting diodes (µLEDs). A longer periphery resulted in a higher light extraction efficiency ( η e ) via the sidewall regardless of the area of the µLEDs. However, as the injection current increased a somewhat larger efficiency droop was observed at the longer periphery due to current crowding. Additionally, larger µLEDs experienced more self-heating than smaller ones, resulting in a red shift of wavelengths and a larger efficiency droop. When the current density exceeded 100 A cm−2, the EQE ratio of smaller-area μLEDs to larger-area ones increased significantly due to the difference in efficiency droop. Besides, a short light propagation length and a long emission width yielded a higher η e . Hence, the periphery, width, length and area of the µLEDs determine EQE, which provides insight into the pixel design of µLED displays.

DOI： 10.1088/1361-6641/ad0b88

Temperature Dependence of α-Particle Detection Performance of GaN PIN Diode Detector Reviewed Open Access

Nakagawa, H; Hayashi, K; Miyazawa, A; Honda, Y; Amano, H; Aoki, T; Nakano, T

SENSORS AND MATERIALS Vol. 36 ( 1 ) page： 169 - 176 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Sensors and Materials

Group-III nitride semiconductors, such as gallium nitride (GaN), have been proposed as novel materials for radiation detection owing to their wide bandgap and their ability to operate at high temperatures. In this study, the radiation detection properties of GaN PIN diode detectors were evaluated at high temperatures (~573 K). The energy spectrum peak profiles of241Am α-particles were obtained at different temperatures, confirming the operation of GaN PIN diodes up to 573 K. The peak positions shifted toward the lower-energy side and the full width at half maximum (FWHM) of the detection energy peak improved with increasing temperature. Furthermore, the variation in electron carrier mobility–lifetime product (μeτe) between 293 and 573 K was not significant. These results indicate the potential high-temperature operation of group-III nitride semiconductors. Additionally, the variation in each detection characteristic was caused by increasing the atmospheric temperature, which affected the mobility, lattice scattering, bandgap, and built-in potential differently.

DOI： 10.18494/SAM4647

Light-Stimulated Artificial Synapses with Accelerating Photopic Adaption Based on III-Nitride Heterojunction Transistor Reviewed

Yan J., Sun Z., Fang L., Yan Y., Shi Z., Shi F., Jiang C., Choi H.W., Amano H., Liu Y., Wang Y.

ACS Photonics 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Photonics

Neuromorphic computing, inspired by biological synapses, has emerged as a pivotal approach to overcome the limitations of von Neumann architecture. In this work, we employ a three-terminal III-nitride metal-oxide-semiconductor field-effect transistor (MOSFET) structure based on the GaN-on-silicon platform, characterized by ultralow power consumption, to emulate artificial synapses through light stimulation. Remarkably, our device exhibits a minimal power consumption of 7 fJ per synaptic event, surpassing that of biological synapses (∼10 fJ). Notably, we observe that the paired pulse facilitation (PPF) index can be modulated by the external light intensity, pulse width, and light pulse interval. By manipulating the light intensity and pulse width, we achieve a PPF index exceeding 300% in our device. Furthermore, our devices demonstrate gate-tunable synaptic plasticity, enabling electric/light cooperative control and increasing the tuning freedom. Finally, acceleration of photopic adaption and a 91.28% handwritten digit recognition accuracy are achieved, which provide strong support in potential visual sensory applications.

DOI： 10.1021/acsphotonics.4c01038

SEM imaging of high aspect ratio trench by selectively controlling the electron beam irradiation using photocathode Reviewed

Arakawa, Y; Niimi, K; Otsuka, Y; Sato, D; Koizumi, A; Shikano, H; Iijima, H; Nishitani, T; Honda, Y; Amano, H

METROLOGY, INSPECTION, AND PROCESS CONTROL XXXVIII Vol. 12955 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

Observation of high aspect ratio (HAR) structures is a difficult challenge in metrology and inspection in semiconductor manufacturing. In imaging HAR trenches using a scanning electron microscope (SEM), obtaining SEM images without information loss due to whiteouts and blackouts is challenging. One reason for the difficulty is that the probe current is constant in conventional SEM imaging. Suppose the probe current is increased to detect more secondary electrons from the bottom of the trench. In that case, excessive secondary electron emission from the top of the trench will result in a whiteout. The SEM equipped with a photocathode electron gun (PC-SEM) can change the probe current on a pixel-by-pixel basis by applying a pulsed electron beam. In this study, we propose two methods of SEM observation for HAR trenches. The first method uses a lower probe current at the top of the trench and a higher probe current at the bottom. With this method, the top and bottom of the trench could be observed simultaneously without any whiteout or blackout. Another method is to adjust the probe current so that the SEM image is in a constant grayscale. In this case, information about the sample appears in the probe current. The image of the probe current captured the trench bottom more clearly than the conventional SEM image under equivalent conditions.

DOI： 10.1117/12.3010733

Photoelectron beam from semiconductor photocathodes leading to new inspection technologies

Nishitani T., Arakawa Y., Niimi K., Otsuka Y., Sato D., Koizumi A., Shikano H., Iijima H., Honda Y., Amano H.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 12955 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

Semiconductor photocathodes are electron beam sources with versatile electron beam performance such as pulsed structure as well as high beam current with high monochromaticity. Photocathode using GaN semiconductor material has solved the durability problem, resulting in the development of a compact photocathode electron gun suitable for industrial technology. The photocathode electron gun can be retrofitted to existing electron microscopes, has the same brightness as a cold field emitter cathode, and the pulsed beam not only brings selective beam irradiation to arbitrary area in the field of view in SEM imaging, but also allows blur-free TEM imaging of moving samples.

DOI： 10.1117/12.3010730

Local voltage contrast changes in MOSFET using scanning electron microscopy with photoelectron beam technology

Sato, D; Arakawa, Y; Niimi, K; Fukuroi, K; Tajiri, Y; Koizumi, A; Shikano, H; Iijima, H; Nishitani, T; Honda, Y; Amano, H

METROLOGY, INSPECTION, AND PROCESS CONTROL XXXVIII Vol. 12955 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

Scanning electron microscopy (SEM) is used for metrology and inspection in semiconductor manufacturing. In addition, electrical defects such as short circuits and unintentional insulation appear as contrast differences called voltage contrast (VC) in SEM under low acceleration voltage conditions. Moreover, by using pulsed electron beams from a photocathode, the probe current can be arbitrarily changed by pixel in the SEM image. Using this technology, we succeeded in observing the change in the VC of the drain in the metal-oxide-semiconductor field effect transistor (MOSFET) by changing in electron beam irradiation on the gate only. In this study, to estimate the threshold voltage of n-type MOSFET (nMOS) from VC, we investigated quantitative changes in the specimen current of the drain (Id) and the gate (Ig) due to gate e-beam irradiation ON/OFF during SEM imaging. The landing energy of the electron beam was set to 0.8 keV, the probe current was 6.3 pA, and the e-beam was irradiated onto only the gate and drain electrodes. Id and Ig, which showed a positive value at the beginning, decreased with time, and saturated at negative values. When the electron beam irradiation to the gate was turned OFF, the Id decreased further and reached saturation. When the gate e-beam irradiation was turned ON again, Ig recovered to a positive and then saturated again to a negative value. On the other hand, the drain Id increased when the gate irradiation was turned ON and returned to the same value as before it was turned OFF.

DOI： 10.1117/12.3009947

UV-C Wavelengths Laser Diode Using Single-Crystal AlN Substrate Open Access

ZHANG Ziyi, KUSHIMOTO Maki, YOSHIKAWA Akira, SASAOKA Chiaki, SCHOWALTER Leo J., AMANO Hiroshi

The Review of Laser Engineering Vol. 52 ( 1 ) page： 6 2024

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Laser Society of Japan

The development of laser diodes (LDs) in the deep-ultraviolet (UV-C) wavelengths has been progressing
rapidly in recent years. Our research group has demonstrated room-temperature continuous lasing of
LDs in the 270-nm UV-C wavelength band. This article describes, the key technologies for achieving
UV-C LDs: the control of p-type conductivity of AlGaN with high Al composition by polarization doping,
and the pseudomorphic growth of AlGaN heterostructure using AlN single-crystal substrates.

DOI： 10.2184/lsj.52.1_6

Anisotropic hole transport along [0001] and [1120] direction in p-doped (1010) GaN Reviewed Open Access

Lin, YY; Wang, J; Pristovsek, M; Honda, Y; Amano, H

JOURNAL OF APPLIED PHYSICS Vol. 134 ( 23 ) 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

The anisotropic hole transport along [0001] and [1120] in the p-doped (1010) GaN layer was compared for layers grown on bulk (1010) GaN substrates and on (1010) sapphire. The sheet resistance along [0001] was 1.1 times larger on GaN substrates and even 1.2 times larger on sapphire than that along [1120]. The anisotropic hole transport on bulk GaN substrates is due to the anisotropy of the hole’s effective mass and the different contribution of carriers in different bands, whereas the larger anisotropy for GaN on sapphire is also due to additional scattering at stacking faults. The annealing process of metal Mg applied to the m-plane p-type GaN successfully results in a robust p-type ohmic contact, functioning as a p++ layer.

DOI： 10.1063/5.0177681

Electron lifetime and diffusion coefficient in dopant-free p-type distributed polarization doped AlGaN Reviewed Open Access

Kumabe, T; Kawasaki, S; Watanabe, H; Honda, Y; Amano, H

APPLIED PHYSICS LETTERS Vol. 123 ( 25 ) 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Minority carrier properties in dopant-free p-type distributed polarization doped (DPD) AlGaN layers were investigated on the basis of the forward-biased current density-voltage (J-V) characteristics of p-n+ diodes. The fabricated p-DPD AlGaN/n+-AlGaN:Si diodes exhibited ideal electrical characteristics despite the absence of acceptor atoms in the p-type layer. The extracted Shockley-Read-Hall lifetime exceeded 300 ps, which was longer than that reported for p-GaN:Mg on GaN substrates with a similar acceptor concentration (20-50 ps). Moreover, the electron diffusion coefficient was about 20 cm2 s−1 at any temperature, which was convincing in terms of the electron mobility in DPD layers. The results suggest that p-DPD AlGaN has more desirable minority carrier properties than conventional p-GaN:Mg, particularly for bipolar device applications.

DOI： 10.1063/5.0180062

Ga-polar GaN Camel diode enabled by a low-cost Mg-diffusion process Reviewed Open Access

Sarkar, B; Wang, J; Badami, O; Pramanik, T; Kwon, W; Watanabe, H; Amano, H

APPLIED PHYSICS EXPRESS Vol. 16 ( 12 ) 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

In this letter, we show that low-cost physical vapor deposition of Mg followed by a thermal diffusion annealing process increases the effective barrier height at the metal/Ga-polar GaN Schottky interface. Thus, for the first time, GaN Camel diodes with improved barrier height and turn-on voltage were realized compared to regular GaN Schottky barrier diodes. Temperature-dependent current-voltage characteristics indicated a near-homogeneous and near-ideal behavior of the GaN Camel diode. The analysis performed in this work is thought to be promising for improving the performance of future GaN-based unipolar diodes.

DOI： 10.35848/1882-0786/ad0db9

Using low-temperature growth to resolve the composition pulling effect of UV-C LEDs Reviewed Open Access

Yoshikawa, A; Zhang, ZY; Kushimoto, M; Aoto, K; Sasaoka, C; Amano, H

APPLIED PHYSICS LETTERS Vol. 123 ( 22 ) 2023.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

One approach to improving the output power of ultraviolet (UV-C) light-emitting diodes (LEDs) is to adopt an electron-blocking layer (EBL) with a high barrier. However, the intended effect may not be realized because of the composition pulling effect, which is the unintended occurrence of a gradient layer at an AlGaN/AlGaN hetero-interface with substantial differences in the Al composition. Here, we demonstrate that low-temperature growth (i.e., <1000 °C) can be used to control the unintentional gradient layer at an AlN/AlGaN hetero-interface between a barrier layer and AlN-EBL with a difference in Al compositions of more than 30%. LEDs with an emission wavelength of 265 nm were fabricated, and an AlN-EBL was grown at low temperature to realize an abrupt interface. At an applied current of 100 mA, growing the EBL under low-temperature conditions improved the forward voltage by 0.5 V and remarkably improved the peak luminous intensity by 1.4-1.6 times. Our results can be used to realize UV-C LEDs with a steep EBL and further improve their device characteristics.

DOI： 10.1063/5.0183320

Multiplexing of bias-controlled modulation modes on a monolithic III-nitride optoelectronic chip Reviewed

Zhang, H; Ye, ZQ; Yan, JB; Shi, F; Shi, ZM; Li, DB; Liu, YH; Amano, H; Wang, YJ

OPTICS LETTERS Vol. 48 ( 19 ) page： 5069 - 5072 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Optics Letters

III-nitride optoelectronic chips have tremendous potential for developing integrated computing and communication systems with low power consumption. The monolithic, top–down approaches are advantageous for simplifying the fabrication process and reducing the corresponding manufacturing cost. Herein, an ultraviolet optical interconnection system is investigated to discover the way of multiplexing between emission and absorption modulations on a monolithic optoelectronic chip. All on-chip components, the transmitter, monitor, waveguide, modulator, and receiver, share the same quantum well structure. As an example, two bias-controlled modulation modes are used to modulate video and audio signals in the experiment presented in this Letter. The results show that our on-chip optoelectronic system works efficiently in the near ultraviolet band, revealing the potential breadth of GaN optoelectronic integration.

DOI： 10.1364/OL.503429

Dislocation Suppresses Sidewall-Surface Recombination of Micro-LEDs Reviewed

Park, JH; Pristovsek, M; Cai, WT; Cheong, HJ; Kang, CM; Lee, DS; Seong, TY; Amano, H

LASER & PHOTONICS REVIEWS Vol. 17 ( 10 ) 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Laser and Photonics Reviews

Nonradiative recombination rate that consists of dislocation-related nonradiative recombination rate (A0) and surface recombination rate (As) is one of the major parameters determining the performance of microlight-emitting diodes (µLEDs). Recent demonstrations improving the efficiency of blue InGaN or red AlGaInP µLEDs using specific methods such as atomic layer deposition or chemical treatment confirm the suppression of As. However, it is hardly found that those methods effectively improve the efficiency of red InGaN µLEDs so far. Here, it is discovered that the dislocation leads to an ineffective As. First, an intrinsic As degrades the external quantum efficiency (EQE) of blue InGaN µLEDs, resulting in EQE decreases with shrinking size. Second, panchromatic cathodoluminescence finds evidence that most of the carriers can be trapped before reaching the sidewall due to high A0. This results in shortened diffusion length of carriers and reduces the number of carriers reaching the sidewall. Consequently, the opposite trend of increasing EQE with shrinking size occurs in the case of red InGaN µLEDs due to an ineffective As. Furthermore, an 8.3 nm quantum well of InGaN with 13% Indium content that can reach a ≈690 nm wavelength at the low current is shown.

DOI： 10.1002/lpor.202300199

UV/DUV light emitters Reviewed Open Access

Khan, A; Kneissl, M; Amano, H

APPLIED PHYSICS LETTERS Vol. 123 ( 12 ) 2023.9

Impact of graphene state on the orientation of III-nitride Reviewed

Park, JH; Hu, N; Park, MD; Wang, J; Yang, X; Lee, DS; Amano, H; Pristovsek, M

APPLIED PHYSICS LETTERS Vol. 123 ( 12 ) 2023.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We attempted to grow (10-13) semi-polar GaN on graphene to confirm the possibility of a remote epitaxy of semi-polar GaN. Single crystalline (10-13) GaN was obtained on an optimized template using optimized growth conditions. However, (10-13), (0002), and other GaN orientations were found under the same growth conditions on a graphene-coated template. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy revealed that multi-domain GaN and (0002) GaN occurred in areas with a damaged graphene interfacial layer and intact graphene, respectively. Raman spectroscopy confirmed that graphene could survive under the growth conditions used here. Using cross-sectional scanning electron microscopy, we propose a simple approach to distinguish damaged graphene. Although the remote epitaxy of semi-polar GaN has not been demonstrated despite the usage of an optimized template and growth conditions, our results confirm the importance of the interfacial state in determining the crystallinity of the overgrown layer.

DOI： 10.1063/5.0157588

Investigation of Electrical Properties of N-Polar AlGaN/AlN Heterostructure Field-Effect Transistors Reviewed

Inahara, D; Matsuda, S; Matsumura, W; Okuno, R; Hanasaku, K; Kowaki, T; Miyamoto, M; Yao, YZ; Ishikawa, Y; Tanaka, A; Honda, Y; Nitta, S; Amano, H; Kurai, S; Okada, N; Yamada, Y

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 220 ( 16 ) 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

AlN-based field-effect transistors (FETs) enable high-breakdown voltage, high drain current, and high-temperature operation. To realize high-frequency devices, N-polar AlGaN/AlN heterostructure FETs are focused on. N-polar Al0.1Ga0.9N/Al0.9Ga0.1N/AlN FET is fabricated using metal–organic vapor-phase epitaxy, and its electrical characteristics are evaluated. An N-polar AlN layer is grown on a sapphire substrate with a misorientation angle of 2.0° toward m-axis, on which a 20 nm thick Al0.9Ga0.1N base layer and a 20 nm Al0.1Ga0.9N channel layer are grown. The static FET operation is confirmed to exhibit an n-channel and pinch-off. Normally, during operation with a turn-on voltage of −3.2 V, a high operating breakdown voltage of 620 V and high operating temperature of 280 °C are also confirmed.

DOI： 10.1002/pssa.202200871

Inactivation characteristics of a 280 nm Deep-UV irradiation dose on aerosolized SARS-CoV-2 Reviewed Open Access

Takamure, K; Iwatani, Y; Amano, H; Yagi, T; Uchiyama, T

ENVIRONMENT INTERNATIONAL Vol. 177 page： 108022 2023.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Environment International

A non-filter virus inactivation unit was developed that can control the irradiation dose of aerosolized viruses by controlling the lighting pattern of a 280 nm deep-UV (DUV)-LED and the air flowrate. In this study, the inactivation properties of aerosolized SARS-CoV-2 were quantitatively evaluated by controlling the irradiation dose to the virus inside the inactivation unit. The RNA concentration of SARS-CoV-2 remained constant when the total irradiation dose of DUV irradiation to the virus exceeded 16.5 mJ/cm2. This observation suggests that RNA damage may occur in regions below the detection threshold of RT-qPCR assay. However, when the total irradiation dose was less than 16.5 mJ/cm2, the RNA concentration monotonically increased with a decreasing LED irradiation dose. However, the nucleocapsid protein concentration of SARS-CoV-2 was not predominantly dependent on the LED irradiation dose. The plaque assay showed that 99.16% of the virus was inactivated at 8.1 mJ/cm2 of irradiation, and no virus was detected at 12.2 mJ/cm2 of irradiation, resulting in a 99.89% virus inactivation rate. Thus, an irradiation dose of 23% of the maximal irradiation capacity of the virus inactivation unit can activate more than 99% of SARS-CoV-2. These findings are expected to enhance versatility in various applications. The downsizing achieved in our study renders the technology apt for installation in narrow spaces, while the enhanced flowrates establish its viability for implementation in larger facilities.

DOI： 10.1016/j.envint.2023.108022

Stress relaxation of AlGaN on nonpolar m-plane GaN substrate Reviewed Open Access

Lin, YY; Sena, H; Frentrup, M; Pristovsek, M; Honda, Y; Amano, H

JOURNAL OF APPLIED PHYSICS Vol. 133 ( 22 ) 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

The stress relaxation with increasing thickness of metal-organic vapor phase epitaxy grown Al0.19Ga0.81N on quasi-bulk (101 ¯0) m-plane GaN substrates was investigated by x-ray diffraction. The anisotropic in-plane stress leads to an orthorhombic distortion of the lattice, which requires special mathematical treatment. Extending earlier works, we developed a method to calculate the distortion along [12 ¯10], [0001], and [101 ¯0] and obtained the lattice parameters, Al content, and strain values. The stress relaxation along the two in-plane directions involves two different mechanisms. First, the stress along [12 ¯10] relaxes by the onset of misfit dislocations through the { 10 1 ¯ 0 } ⟨ 1 2 ¯ 10 ⟩ slip system while for thicker layers the stress along [0001] relaxes by crack formation. Comparing the cathodoluminescence emission at room temperature with the expected bandgap showed that both tensile in-plane strains along [12 ¯10] and [0001] decrease the bandgap.

DOI： 10.1063/5.0149838

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro-LEDs Reviewed Open Access

Park, JH; Pristovsek, M; Cai, WT; Cheong, HJ; Tanaka, A; Furusawa, Y; Han, DP; Seong, TY; Amano, H

ADVANCED OPTICAL MATERIALS Vol. 11 ( 10 ) 2023.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Advanced Optical Materials

The sidewall condition is a key factor determining the performance of micro-light emitting diodes (µLEDs). In this study, equilateral triangular III-nitride blue µLEDs are prepared with exclusively m-plane sidewall surfaces to confirm the impact of sidewall conditions. It is found that inductively coupled plasma-reactive ion etching (ICP-RIE) causes surface damages to the sidewall and results in rough surface morphology. As confirmed by time-resolved photoluminescence (TRPL) and X-ray photoemission spectroscopy (XPS), tetramethylammonium hydroxide (TMAH) eliminates the etching damage and flattens the sidewall surface. After ICP-RIE, 100 µm2-µLEDs yield higher external quantum efficiency (EQE) than 400 µm2-µLEDs. However, after TMAH treatment, the peak EQE of 400 µm2-µLEDs increases by ≈10% in the low current regime, whereas that of 100 µm2-µLEDs slightly decreases by ≈3%. The EQE of the 100 µm2-µLEDs decreases after TMAH treatment although the internal quantum efficiency (IQE) increases. Further, the IQE of the 100 µm2-µLEDs before and after TMAH treatment is insignificant at temperatures below 150 K, above which it becomes considerable. Based on PL, XPS, scanning transmission electron microscopy, and scanning electron microscopy results, mechanisms for the size dependence of the EQE of µLEDs are explained in terms of non-radiative recombination rate and light extraction.

DOI： 10.1002/adom.202203128

Lateral p-type GaN Schottky barrier diode with annealed Mg ohmic contact layer demonstrating ideal current-voltage characteristic Reviewed

Lu, S; Deki, M; Kumabe, T; Wang, J; Ohnishi, K; Watanabe, H; Nitta, S; Honda, Y; Amano, H

APPLIED PHYSICS LETTERS Vol. 122 ( 14 ) 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We have demonstrated the fabrication process for a lateral p-type Schottky barrier diode (SBD) with the annealed Mg ohmic contact layer on a MOVPE-grown p-GaN wafer and measured the electrical characteristic of the diode. Because of the selective-area ohmic contact, the interface between the Schottky electrode and p-type GaN is well protected from any damage introduced by dry-etching or regrowth. The ideality factor of the forward current-voltage characteristic is as low as 1.09 at room temperature and an on-off ratio above 109 is also achieved. Various metals are deposited as the Schottky electrode and the work function dependence of the Schottky barrier height is confirmed with a pinning factor of 0.58. The temperature dependence of the current-voltage characteristic indicates that the GaN p-type SBD still fits the thermionic emission mode at 600 K with an ideality factor of 1.1. The reverse current of the p-SBD is also studied with the Poole-Frenkel emission model, and the trap energy level in the p-GaN is confirmed.

DOI： 10.1063/5.0146080

Simultaneous light emission and detection of an AlGaInP quantum well diode Reviewed Open Access

Ye, ZQ; Zhang, H; Gao, XM; Fu, K; Zeng, HB; Liu, YH; Wang, YJ; Amano, H

AIP ADVANCES Vol. 13 ( 4 ) 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Advances

When a quantum well (QW) diode is biased with a forward voltage and illuminated with an external shorter-wavelength light, the device simultaneously emits and detects light, with the injected current and the induced current mixed inside the wells. Separating these superimposed and dynamic electrical signals is useful for the development of multifunctional displays that can simultaneously transmit and receive light signals. By utilizing the unique overlap between the electroluminescence and detection spectra, we establish a wireless optical communication system using two AlGaInP diodes that have identical QW structures. The communication distance is 25 m, with one diode functioning as the transmitter and the other as the receiver. In particular, at the receiver end, the QW diode demonstrates simultaneous light emission and reception ability, and the mixed signals can be efficiently extracted, suggesting great potential for applications from light communication to advanced displays.

DOI： 10.1063/5.0142093

2D-GaN/AlN Multiple Quantum Disks/Quantum Well Heterostructures for High-Power Electron-Beam Pumped UVC Emitters. Reviewed Open Access

Jmerik V, Nechaev D, Semenov A, Evropeitsev E, Shubina T, Toropov A, Yagovkina M, Alekseev P, Borodin B, Orekhova K, Kozlovsky V, Zverev M, Gamov N, Wang T, Wang X, Pristovsek M, Amano H, Ivanov S

Nanomaterials (Basel, Switzerland) Vol. 13 ( 6 ) 2023.3

A Review on the Progress of AlGaN Tunnel Homojunction Deep-Ultraviolet Light-Emitting Diodes Invited Reviewed Open Access

Nagata, K; Matsubara, T; Saito, Y; Kataoka, K; Narita, T; Horibuchi, K; Kushimoto, M; Tomai, S; Katsumata, S; Honda, Y; Takeuchi, T; Amano, H

CRYSTALS Vol. 13 ( 3 ) 2023.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Crystals

Conventional deep-ultraviolet (UV) light-emitting diodes (LEDs) based on AlGaN crystals have extremely low light-emission efficiencies due to the absorption in p-type GaN anode contacts. UV-light-transparent anode structures are considered as one of the solutions to increase a light output power. To this end, the present study focuses on developing a transparent AlGaN homoepitaxial tunnel junction (TJ) as the anode of a deep-UV LED. Deep-UV LEDs composed of n+/p+-type AlGaN TJs were fabricated under the growth condition that reduced the carrier compensation in the n+-type AlGaN layers. The developed deep-UV LED achieved an operating voltage of 10.8 V under a direct current (DC) operation of 63 A cm−2, which is one of the lowest values among devices composed of AlGaN tunnel homojunctions. In addition, magnesium zinc oxide (MgZnO)/Al reflective electrodes were fabricated to enhance the output power of the AlGaN homoepitaxial TJ LED. The output power was increased to 57.3 mW under a 63 A cm−2 DC operation, which was 1.7 times higher than that achieved using the conventional Ti/Al electrodes. The combination of the AlGaN-based TJ and MgZnO/Al reflective contact allows further improvement of the light output power. This study confirms that the AlGaN TJ is a promising UV-transmittance structure that can achieve a high light-extraction efficiency.

DOI： 10.3390/cryst13030524

Temperature Field, Flow Field, and Temporal Fluctuations Thereof in Ammonothermal Growth of Bulk GaN-Transition from Dissolution Stage to Growth Stage Conditions. Reviewed Open Access

Schimmel S, Tomida D, Ishiguro T, Honda Y, Chichibu SF, Amano H

Materials (Basel, Switzerland) Vol. 16 ( 5 ) 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials

With the ammonothermal method, one of the most promising technologies for scalable, cost-effective production of bulk single crystals of the wide bandgap semiconductor GaN is investigated. Specifically, etch-back and growth conditions, as well as the transition from the former to the latter, are studied using a 2D axis symmetrical numerical model. In addition, experimental crystal growth results are analyzed in terms of etch-back and crystal growth rates as a function of vertical seed position. The numerical results of internal process conditions are discussed. Variations along the vertical axis of the autoclave are analyzed using both numerical and experimental data. During the transition from quasi-stable conditions of the dissolution stage (etch-back process) to quasi-stable conditions of the growth stage, significant temperature differences of 20 K to 70 K (depending on vertical position) occur temporarily between the crystals and the surrounding fluid. These lead to maximum rates of seed temperature change of 2.5 K/min to 1.2 K/min depending on vertical position. Based on temperature differences between seeds, fluid, and autoclave wall upon the end of the set temperature inversion process, deposition of GaN is expected to be favored on the bottom seed. The temporarily observed differences between the mean temperature of each crystal and its fluid surrounding diminish about 2 h after reaching constant set temperatures imposed at the outer autoclave wall, whereas approximately quasi-stable conditions are reached about 3 h after reaching constant set temperatures. Short-term fluctuations in temperature are mostly due to fluctuations in velocity magnitude, usually with only minor variations in the flow direction.

DOI： 10.3390/ma16052016

Red emission from InGaN active layer grown on nanoscale InGaN pseudosubstrates Reviewed

Cai, WT; Wang, J; Park, JH; Furusawa, Y; Cheong, HJ; Nitta, S; Honda, Y; Pristovsek, M; Amano, H

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 62 ( 2 ) 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

We demonstrated nanoplatelet In x Ga1−x N pseudosubstrates with In content varying from 0 to 0.3 on low-dislocation-density GaN substrates. These nanoplatelets efficiently relax in-plane strain, thus allowing for the use of a thick active layer to reduce built-in polarization. The 15 nm thick InGaN active layers grown under the same conditions on these nanoplatelets showed a remarkable cathodoluminescence redshift from 460 to 617 nm, suggesting enhanced In incorporation efficiency in InGaN nanoplatelets with higher In content. Moreover, the 617 nm-emitting sample presented an imperceptible blueshift under excitation-power-dependent photoluminescence, indicating a weak polarization field introduced by the high-In-content pseudosubstrates and the thick active layer.

DOI： 10.35848/1347-4065/acb74c

Particle Collection Characteristics of Electrostatic Precipitator with Flat Plate Collection Electrodes Open Access

TAKAMURE Kotaro, IWATANI Yasumasa, AMANO Hiroshi, YAGI Tetsuya, UCHIYAMA Tomomi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2023 ( 0 ) page： S054-05 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

An electrostatic precipitator suitable for the collection of aerosol-sized particles is developed. This device is a two-stage electrostatic precipitator divided into a corona discharge part and a collection electrode part. Positive ion is charged to the virus particles by corona discharge, and the negative pole of the collection electrode installed in the later stage collects these particles. The particle collection performance of the system is investigated when the inlet velocity (inlet flowrate) is varied. As a result, even at the same inlet velocity, the collection rate increased with smaller particle size. Furthermore, the collection efficiency of particles decreased with increasing flow velocity.

DOI： 10.1299/jsmemecj.2023.s054-05

Numerical simulation and validation of carbon incorporation in GaN epitaxial growth by MOVPE method Open Access

MUKAIYAMA Yuji, WATANABE Hirotaka, NITTA Shugo, IIZUKA Masaya, AMANO Hiroshi

The Proceedings of The Computational Mechanics Conference Vol. 2023.36 ( 0 ) page： OS-1406 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

One of the crucial challenges in GaN epitaxial growth by metalorganic vapor phase epitaxy (MOVPE) method is the control of carbon (C) incorporation, which affects the resistivity of the individual layer of high-power and high-frequency devices based on GaN. Incorporating C into the GaN epilayer depends on various process parameters, such as growth temperature, pressure, carrier gas, flow rates of source gases, and reactor type. To determine the process parameters that control incorporated C concentration and uniformity, we have developed a novel numerical model for C incorporation into the grown GaN epilayer using MOVPE method. The developed model considers C incorporation through the decomposition of Ga source gas. We have implemented this model in a commercial crystal growth simulator, Virtual Reactor Nitride Edition, developed by STR. This study used experimental data to evaluate the dependence of temperature, growth rate, and V/III ratio of C incorporation predicted by the simulations. These results showed a strong correlation between the C concentration and these parameters, and good agreement with the experimental data.

DOI： 10.1299/jsmecmd.2023.36.os-1406

Metal Stop Laser Drilling for Blind via Holes of GaN-on-GaN Devices Reviewed Open Access

Sasaoka C., Ando Y., Takahashi H., Ikarashi N., Amano H.

Physica Status Solidi (A) Applications and Materials Science 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

The metal stop laser drilling of GaN-on-GaN devices is demonstrated using a UV sub-nanosecond laser as a light source. By monitoring the Bremsstrahlung emission at the drilling point, metal stops with a precision higher than 1 μm are realized for vias with a depth of 100 μm. From in situ laser-induced breakdown spectroscopy measurements, it is shown that endpoint detection is realized with high signal-to-noise ratio owing to the difference in the emission process between the strongly excited semiconductor and the metal. Herein, a through-substrate electrode with a resistance of less than 5 mΩ on GaN-on-GaN high-electron-mobility transistor (HEMT) wafers is demonstrated. The fabrication of through-substrate electrodes by this technique provides a simple process that does not require lithography or other complex processes. This process is expected to be useful in the fabrication of future GaN-on-GaN devices, including very thin GaN-on-GaN HEMTs.

DOI： 10.1002/pssa.202200739

Photoelectron beam technology for SEM imaging with pixel-specific control of irradiation beam current

Nishitani T., Arakawa Y., Noda S., Koizumi A., Sato D., Shikano H., Iijima H., Honda Y., Amano H.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 12496 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

The scanning electron microscope (SEM) with photocathode technology was launched by retrofitting the photocathode electron gun to a commercial-based SEM system. In this SEM system, the excitation laser for photoelectron generation from the photocathode is synchronized to the scanning signal. SEM images were obtained by high-speed modulation of the photoelectron beam current using the photocathode SEM, where the location in the field of view and its irradiation current were arbitrarily selected on a pixel-by-pixel basis (Selective e-Beaming technology). As a demonstration experiment contributing to non-contact electrical inspection, low-voltage SEM imaging of MOS-FET structures in 3D-NAND flash memory was performed using this selective e-beam technology. As a result, changes in the voltage contrast of the drain electrode were observed in response to on/off selective electron beam irradiation to the gate electrode in the MOS-FET structure. As an extension of the selective electron beaming technology, a Yield Controlled e-beaming (YCeB) technology was invented to control the secondary electron yield generated in the entire field of view of the SEM image by feedback control of the laser power irradiating the photocathode to the intensity of each pixel in the SEM image. The YCeB image, in which the laser power intensity corresponding to the probe intensity is modulated so that the secondary electron yield generated in the entire field of view of the SEM image is constant, is a clearer image with less noise than the original SEM image.

DOI： 10.1117/12.2657853

Novel Electron Beam Technology using InGaN Photocathode for High-Throughput Scanning Electron Microscope Imaging

Sato, D; Koizumi, A; Shikano, H; Noda, S; Otsuka, Y; Yasufuku, D; Mori, K; Iijima, H; Nishitani, T; Honda, Y; Amano, H

METROLOGY, INSPECTION, AND PROCESS CONTROL XXXVII Vol. 12496 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

An InGaN photocathode with a negative electron affinity (NEA) surface is suitable for industrial use because of features such as a long quantum efficiency lifetime, availability with a visible laser as an excitation light source, and the presence of a transmission-type structure. The first objective is the development of an InGaN photocathode electron gun that can be mounted on a scanning electron microscope (SEM) and the evaluation of the electron beam size at the emission point, maximum emission current, and transverse energy of the electron beam, which are important factors for realizing a high probe current in the SEM. The second objective is the evaluation of emission current stability, while the third objective is the generation of a pulsed electron beam and multi-electron beam from the InGaN photocathode. The parameters of the electron beam from the photocathode electron gun were an emission beam radius of 1 µm, transverse energy of 44 meV, and an emission current of up to 110 µA. Using a high beam current with low transverse energy from the photocathode, a 13 nA probe current with 10 nm SEM resolution was observed with 15 µA emission. At 15 µA, the continuous electron beam emission for 1300 h was confirmed; at 30 µA, the cycle time between the NEA surface reactivations was confirmed to be 90 h with 0.043% stability. Moreover, a 4.4 ns pulsed e-beam with a 4.7 mA beam current was generated, and a 5 × 5 multielectron beam with 12% uniformity was then obtained. The advantages of the InGaN photocathode, such as high electron beam current, low transverse energy, long quantum efficiency lifetime, pulsed electron beam, and multi-electron beam, are useful in industries including semiconductor device inspection tools.

DOI： 10.1117/12.2657032

Development in AlGaN homojunction tunnel junction deep UV LEDs

Nagata K., Anada S., Saito Y., Kushimoto M., Honda Y., Takeuchi T., Amano H.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 12441 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

To reduce the operating voltage, we analyzed the p-n junction of an aluminum gallium nitride (AlGaN) homojunction tunnel junction (TJ) deep-ultraviolet light-emitting diode using phase-shifting electron holography. We obtained a phase image reflecting the band alignment of the p-n homojunction and derived a depletion layer width of approximately 10 nm. We found the AlGaN homojunction TJ forms a p-n junction. Furthermore, the operating voltage reached 8.8 V at 63 A cm-2 by optimizing the structural characteristics of the AlGaN TJ, such as the thickness and impurity concentration, where the thickness of the TJ was 23 nm. We found that the TJ thickness should be at least the same as the depletion layer width at the AlGaN TJ.

DOI： 10.1117/12.2646757

Demonstration of AlN-based Vertical p-n Diodes with Dopant-Free Distributed-Polarization Doping

Kumabe T., Yoshikawa A., Kushimoto M., Honda Y., Arai M., Suda J., Amano H.

Technical Digest - International Electron Devices Meeting, IEDM 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Technical Digest - International Electron Devices Meeting, IEDM

Nearly ideal AlN-based vertical p-n diodes are demonstrated on an AIN substrate utilizing dopant-free distributed-polarization doping (DPD). Capacitance-voltage measurements revealed that the effective doping concentration agreed well with the designed DPD charge concentration. The fabricated devices exhibited a low tum-on voltage of 6.5 V, a low differential specific ON-resistance of 3 mO cm2, and an ideality factor of 2 for a wide range of temperatures (room temperature-573 K). Moreover, the breakdown electric field was 7.3 MV/cm, which was almost twice as high as the reported critical electric field of 4H-SÌC and GaN. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.

DOI： 10.1109/IEDM45741.2023.10413866

Challenges and opportunities of nitride light emitting devices by HVPE thanks to a stable Mg source

Matsumoto K., Ohnishi K., Amano H.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 12441 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

Until recently, lack of stable p-type doping source in HVPE hindered its use to the application of III-nitride light emitting devices. Recently, K. Ohnishi discovered the stable MgO source for p-type doping in GaN HVPE. This has enabled the use of HVPE for light emitting devices as well as electron devices such as vertical MOSFET. In this article, we will review the current HVPE technology of p-GaN HVPE, multi-junction AlInGaP/InGaP/GaAs solar cell, InGaN HVPE by tri-chlorides, and discuss the challenge and opportunities of III-nitride HVPE in terms of epitaxial layer design and the remaining issues of the growth of the low temperature buffer, MQWs as well as the source supply design to grow multilayer structures.

DOI： 10.1117/12.2647336

Evaluation of Switching Characteristics of High Breakdown Voltage GaN-PSJ Transistors at Liquid Nitrogen Temperature

Deki M., Kawarabayashi H., Honda Y., Amano H.

AIAA Aviation and Aeronautics Forum and Exposition, AIAA AVIATION Forum 2023 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：AIAA Aviation and Aeronautics Forum and Exposition, AIAA AVIATION Forum 2023

We demonstrated static characteristics testing and Double-Pulse-Testing (DPT) at 77 K using GaN-Polarization Super Junction (PSJ) transistors, commercialized GaN HEMTs and commercialized SiC-MOSFETs. In the results of SiC-MOSFETs, total switching losses increased at 77 K due to the increase in on-resistance (Ron). On the other hand, in the results of GaN-PSJ transistors, total switching losses decreased at 77 K due to the increase in channel mobilities. In the case of GaN-PSJ transistors, energy losses which are induced self-charging and discharging (Eqoss) in the upper side DUT increased at 77 K. From the measurement of Vds dependence of Cds, Cds increased at 77 K compared with room temperature conditions. However, total switching losses decreased at low temperatures because Eqoss accounts for about 10% of the switching losses.

DOI： 10.2514/6.2023-4538

GaN substrate cut-out process and GaN on GaN device thinning process with laser slicing Open Access

Tanaka A., Matsushima K., Yui T., Aratani T., Hara K., Kawaguchi D., Watanabe H., Kanemura T., Nagasato Y., Nagaya M., Honda Y., Wakejima A., Ando Y., Onda S., Suda J., Amano H.

Cs Mantech 2023 2023 International Conference on Compound Semiconductor Manufacturing Technology 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Cs Mantech 2023 2023 International Conference on Compound Semiconductor Manufacturing Technology

We have developed a technique to slice GaN substrates with reduced kerf loss and processing time with laser. This technique can also be applied to slicing wafers after device fabrication, allowing a thin device layer to be sliced off from the wafer. This means that the electrical and thermal resistance of the devices can be reduced while the base GaN substrate remains reusable. We believe that the use of both wafer and device processing with laser slicing will greatly reduce the cost of GaN substrates in devices. With this technique, we believe that we can realize the practical application of devices using GaN substrates.

Characteristics of collection and inactivation of virus in air flowing inside a winding conduit equipped with 280 nm deep UV-LEDs Open Access

Photon extraction enhancement of praseodymium ions in gallium nitride nanopillars Reviewed Open Access

Sato, SI; Li, S; Greentree, AD; Deki, M; Nishimura, T; Watanabe, H; Nitta, S; Honda, Y; Amano, H; Gibson, BC; Ohshima, T

SCIENTIFIC REPORTS Vol. 12 ( 1 ) page： 21208 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

Lanthanoid-doped Gallium Nitride (GaN) integrated into nanophotonic technologies is a promising candidate for room-temperature quantum photon sources for quantum technology applications. We manufactured praseodymium (Pr)-doped GaN nanopillars of varying size, and showed significantly enhanced room-temperature photon extraction efficiency compared to unstructured Pr-doped GaN. Implanted Pr ions in GaN show two main emission peaks at 650.3 nm and 651.8 nm which are attributed to 3P0-3F2 transition in the 4f-shell. The maximum observed enhancement ratio was 23.5 for 200 nm diameter circular pillars, which can be divided into the emitted photon extraction enhancement by a factor of 4.5 and the photon collection enhancement by a factor of 5.2. The enhancement mechanism is explained by the eigenmode resonance inside the nanopillar. Our study provides a pathway for Lanthanoid-doped GaN nano/micro-scale photon emitters and quantum technology applications.

DOI： 10.1038/s41598-022-25522-6

Takamure, K; Sakamoto, Y; Iwatani, Y; Amano, H; Yagi, T; Uchiyama, T

ENVIRONMENT INTERNATIONAL Vol. 170 page： 107580 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Environment International

A general-purpose virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The inside of the virus inactivation unit is a rectangular conduit with a sharp turn of 180° (sharp-turned rectangular conduit). Virus inactivation is attempted by directly irradiating the air passing through the conduit with DUV rays. The flow characteristics of air and virus particles inside the virus inactivation unit were investigated using numerical simulations. The air was locally accelerated at the sharp turn parts and flowed along the partition plate in the sharp-turned rectangular conduit. The aerosol particles moving in the sharp-turned rectangular conduit were greatly bent in orbit at the sharp turn parts, and then rapidly approached the partition plate at the lower part of the conduit. Consequently, many particles collided with the partition plates behind the sharp-turn parts. SARS-CoV-2 virus was nebulized in the virus inactivation unit, and the RNA concentration and virus inactivation rate with and without the emission of DUV-LEDs were measured in the experiment. The concentration of SARS-CoV-2 RNA was reduced to 60% through DUV-LED irradiation. In addition, SARS-CoV-2 passing through the virus inactivation unit was inactivated below the detection limit by the emission of DUV-LEDs. The virus inactivation rate and the value of the detection limit corresponded to 99.38% and 35.36 TCID50/mL, respectively.

DOI： 10.1016/j.envint.2022.107580

Scanning electron microscope imaging by selective e-beaming using photoelectron beams from semiconductor photocathodes Reviewed

Nishitani, T; Arakawa, Y; Noda, S; Koizumi, A; Sato, D; Shikano, H; Iijima, H; Honda, Y; Amano, H

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Vol. 40 ( 6 ) 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology B

Pulsed electron beams from a photocathode using an InGaN semiconductor have brought selectively scanning technology to scanning electron microscopes, where the electron beam irradiation intensity and area can be arbitrarily selected within the field of view in SEM images. The p-type InGaN semiconductor crystals grown in the metalorganic chemical vapor deposition equipment were used as the photocathode material for the electron beam source after the surface was activated to a negative electron affinity state in the electron gun under ultrahigh vacuum. The InGaN semiconductor photocathode produced a pulsed electron beam with a rise and fall time of 3 ns, consistent with the time structure of the irradiated pulsed laser used for the optical excitation of electrons. The InGaN photocathode-based electron gun achieved a total beam operation time of 1300 h at 15 μA beam current with a downtime rate of 4% and a current stability of 0.033% after 23 cycles of surface activation and continuous beam operation. The InGaN photocathode-based electron gun has been installed in the conventional scanning electron microscope by replacing the original field emission gun. SEM imaging was performed by selective electron beaming, in which the scanning signal of the SEM system was synchronized with the laser for photocathode excitation to irradiate arbitrary regions in the SEM image at arbitrary intensity. The accuracy of the selection of regions in the SEM image by the selective electron beam was pixel by pixel at the TV scan speed (80 ns/pix, 25 frame/s) of the SEM.

DOI： 10.1116/6.0002111

Miniature optical fiber curvature sensor via integration with GaN optoelectronics Open Access

Shi F., Zhang H., Ye Z., Tang X., Qin F., Yan J., Gao X., Zhu H., Wang Y., Liu Y., Amano H.

Communications Engineering Vol. 1 ( 1 ) 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Communications Engineering

Optical fiber curvature sensors have been considered as a promising option for human motion detection due to its good toughness, bending flexibility and anti-electromagnetic interference. However, for wearable devices, the miniature configuration is preferred, and a high integration of the light emitter, receiver and guided fiber is essential to configure the miniaturized sensing system. Here, we present a miniaturized curvature sensing system by integrating a GaN-based optoelectronic chip with the plastical optical fiber (POF). The light emitter and detector are fabricated on a GaN-on-sapphire wafer to form a tiny chip sized at 2.5 × 1.5 mm2. The on-chip photodetector (PD) effectively senses the reflected light intensity, extracting information on the fiber bending deformation. A compact curvature sensing system is demonstrated for finger motion detection with movement angles of 30–90° and frequencies of 0.4, 1, and 1.6 Hz. The results show that the monolithically integrated LED and PD chip can be combined with the POF with reliable operation. The demonstration of the monolithically integrated optoelectronic device suggests a promising potential technology for future wearable fiber optical sensor system.

DOI： 10.1038/s44172-022-00049-w

Key temperature-dependent characteristics of AlGaN-based UV-C laser diode and demonstration of room-temperature continuous-wave lasing Reviewed Open Access

Zhang, ZY; Kushimoto, M; Yoshikawa, A; Aoto, K; Sasaoka, C; Schowalter, LJ; Amano, H

APPLIED PHYSICS LETTERS Vol. 121 ( 22 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Although the pulsed operation of AlGaN-based laser diodes at UV-C wavelengths has been confirmed in the previous studies, continuous oscillation without cooling is difficult because of the high operating voltage. In this study, the temperature dependence of key parameters was investigated and their impact on achieving continuous-wave lasing was discussed. A reduction in the threshold voltage was achieved by tapering the sides of the laser diode mesa and reducing the lateral distance between the n- and p-electrodes. As a result, continuous-wave lasing at room temperature was demonstrated at a threshold current density of 4.2 kA / cm 2 and a threshold voltage of 8.7 V.

DOI： 10.1063/5.0124480

Local stress control to suppress dislocation generation for pseudomorphically grown AlGaN UV-C laser diodes Reviewed Open Access

Kushimoto, M; Zhang, ZY; Yoshikawa, A; Aoto, K; Honda, Y; Sasaoka, C; Schowalter, LJ; Amano, H

APPLIED PHYSICS LETTERS Vol. 121 ( 22 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Previously reported UV-C laser diode (LD) structures have been subject to design constraints owing to dark line defects at the edge of the mesa stripe after device fabrication. To address this issue, a detailed analysis revealed that the dark line defects were dislocations generated by local residual shear stresses associated with mesa formation on highly strained epitaxial layers. A technique for controlling the local concentration of shear stress using a sloped mesa geometry was proposed based on insight gained by modeling the stress distribution at the edge of the mesa stripe. Experimental results showed that this technique succeeded in completely suppressing the emergence of dark-line defects. This technique will be useful in improving the performance of pseudomorphic AlGaN/AlN-based optoelectronic devices, including UV-C LDs.

DOI： 10.1063/5.0124512

Electrical Characteristics of Thermally Stable Ag-Pd-Cu Alloy Schottky Contacts on n-Al0.6Ga0.4N Open Access

Sim, KB; Kim, SK; Seong, TY; Amano, H

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 11 ( 11 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ECS Journal of Solid State Science and Technology

We report the fabrication of high-barrier-height and thermally reliable Schottky contacts to n-Al0.6Ga0.4N by using an Ag-Pd-Cu (APC) alloy. The Schottky barrier heights (SBHs) and ideality factors computed using the current-voltage (I-V) model ranged from 0.82 to 0.97 eV and from 3.15 to 3.44, respectively. The barrier inhomogeneity model and capacitance-voltage (C-V) method yielded higher SBHs (1.62-2.19 eV) than those obtained using the I-V model. The 300 °C-annealed APC sample exhibited more uniform electrical characteristics than the 500 °C-annealed Ni/Au Schottky samples (each with the best Schottky behavior). Furthermore, the scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) results indicated that the APC Schottky contacts were more thermally stable than the Ni/Au contacts. On the basis of the X-ray photoemission spectroscopy (XPS) results, the improved Schottky characteristics of the APC alloy contacts are described and discussed.

DOI： 10.1149/2162-8777/aca1df

Substitutional diffusion of Mg into GaN from GaN/Mg mixture Reviewed Open Access

Itoh, Y; Lu, S; Watanabe, H; Deki, M; Nitta, S; Honda, Y; Tanaka, A; Amano, H

APPLIED PHYSICS EXPRESS Vol. 15 ( 11 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

We evaluated Mg-diffusion into GaN from GaN/Mg mixture. The diffusion depth of Mg increased with diffusion temperature from 1100 °C to 1300 °C, whereas the Mg concentration remained constant at 2-3 × 1018 cm−3 independent of temperature. The estimated activation energy for Mg diffusion was 2.8 eV, from which the substitutional diffusion mechanism was predicted. Mg-diffused GaN samples showed p-type conductivity with a maximum hole mobility of 27.7 cm2 V−1 s−1, suggesting that substitutional diffusion contributes to Mg activation. This diffusion technique can be used to easily form p-type GaN and has potential as a p-type selective doping technique.

DOI： 10.35848/1882-0786/ac9c83

Adsorption structure deteriorating negative electron affinity under the H2O environment Reviewed

Kashima, M; Ishiyama, S; Sato, D; Koizumi, A; Iijima, H; Nishitani, T; Honda, Y; Amano, H; Meguro, T

APPLIED PHYSICS LETTERS Vol. 121 ( 18 ) 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Photocathodes with negative electron affinity (NEA) characteristics have various advantages, such as small energy spread, high spin polarization, and ultrashort pulsing. Nitride semiconductors, such as GaN and InGaN, are promising materials for NEA photocathodes because their lifetimes are longer than those of other materials. In order to further prolong the lifetime, it is important to better understand the deterioration of NEA characteristics. The adsorption of residual gases and back-bombardment by ionized residual gases shorten the lifetime. Among the adsorbed residual gases, H2O has a significant influence. However, the adsorption structures produced by the reaction with H2O are not comprehensively studied so far. In this study, we investigated adsorption structures that deteriorated the NEA characteristics by exposing InGaN and GaAs to an H2O environment and discussed the differences in their lifetimes. By comparing the temperature-programmed desorption curves with and without H2O exposure, the generation of CsOH was confirmed. The desorption of CsOH demonstrated different photoemission behaviors between InGaN and GaAs results. InGaN recovered its NEA characteristics, whereas GaAs did not. Considering the Cs desorption spectra, it is difficult for an NEA surface on InGaN to change chemically, whereas that for GaAs changes easily. The chemical reactivity of the NEA surface is different for InGaN and GaAs, which contributes to the duration of photoemission. We have attempted to prolong the lifetime of InGaN by recovering its NEA characteristics. We found that InGaN with NEA characteristics can be reused easily without thermal treatment at high temperatures.

DOI： 10.1063/5.0125344

Monolithic GaN optoelectronic system on a Si substrate Reviewed

Zhang, H; Yan, JB; Ye, ZQ; Shi, F; Piao, JL; Wang, W; Gao, XM; Zhu, HB; Wang, YJ; Liu, YH; Amano, H

APPLIED PHYSICS LETTERS Vol. 121 ( 18 ) 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

GaN-based devices have grown rapidly in recent decades, due to their important research value and application prospects. There is a desire to monolithically integrate different GaN devices into a single chip for the development of future optoelectronic systems with low power consumption. In addition to improved multifunctional performance, a miniature integrated system can result in a significant reduction in material costs, processing costs, and packaging costs. In view of such prospects, we propose monolithic, top-down approaches to build III-nitride transmitter, modulator, waveguide, beam splitter, receiver, and monitor as a single unit onto a conventional GaN-on-silicon wafer without involving regrowth or postgrowth doping. Data communication among these components is realized through light propagation, opening up horizons for GaN optoelectronic systems on a chip.

DOI： 10.1063/5.0125324

The photoemission characteristics of a NEA InGaN photocathode by simultaneously supplying Cs and O2 Reviewed Open Access

Kashima, M; Itokawa, Y; Kanai, T; Sato, D; Koizumi, A; Iijima, H; Nishitani, T; Honda, Y; Amano, H; Meguro, T

APPLIED SURFACE SCIENCE Vol. 599 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

A high quantum efficiency (QE) can be obtained on negative electron affinity (NEA) surfaces. It is well-known that NEA surfaces can be formed on semiconductor materials such as GaAs by the alternating supply of cesium (Cs) and oxygen (O2), which is called the yo-yo method. While GaN and related compounds such as InGaN are expected to realize an NEA photocathode with a long lifetime, the surface reactions between GaAs and nitride semiconductors are completely different with respect to the increasing rate of QE induced by the supply of O2. In addition, the surface processes of photoemission from NEA nitride semiconductors have not yet been elucidated. In the present study, a higher QE was achieved in InGaN by simultaneously supplying Cs and O2 instead of using the conventional yo-yo method. The possible Cs adsorption states in relation to the photoemission are also discussed based on the QE tendencies and the temperature programmed desorption (TPD) spectra of the NEA surfaces formed under elevated temperature conditions. This study suggests that the Cs oxide species, which is one of the key compounds for imparting the NEA nature, decomposes at approximately 350 °C and that the InGaN-Cs2O2 structure is a possible candidate for NEA photocathodes.

DOI： 10.1016/j.apsusc.2022.153882

High-Energy Computed Tomography as a Prospective Tool for In Situ Monitoring of Mass Transfer Processes inside High-Pressure Reactors-A Case Study on Ammonothermal Bulk Crystal Growth of Nitrides including GaN Reviewed Open Access

Schimmel, S; Salamon, M; Tomida, D; Neumeier, S; Ishiguro, T; Honda, Y; Chichibu, SF; Amano, H

MATERIALS Vol. 15 ( 17 ) 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials

For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using high-energy computed tomography for this purpose was therefore evaluated using ex situ measurements. Acceleration voltages of 600 kV were estimated to yield suitable transparency in a lab-scale ammonothermal setup for GaN crystal growth designed for up to 300 MPa operating pressure. The total scan duration was estimated to be in the order of 20 to 40 min, which was sufficient given the comparatively slow crystal growth speed in ammonothermal growth. Even shorter scan durations or, alternatively, lower acceleration voltages for improved contrast or reduced X-ray shielding requirements, were estimated to be feasible in the case of ammonoacidic growth, as the lower pressure requirements for this process variant allow for thinned autoclave walls in an adapted setup designed for improved X-ray transparency. Promising nickel-base and cobalt-base alloys for applications in ammonothermal reactors with reduced X-ray absorption in relation to the maximum operating pressure were identified. The applicability for the validation of numerical simulations of the growth process of GaN, in addition to the applicability of the technique to further nitride materials, as well as larger reactors and bulk crystals, were evaluated.

DOI： 10.3390/ma15176165

Understanding indium incorporation of InGaN grown on polar, semi-polar, and non-polar orientation by metal-organic vapor phase epitaxy Reviewed

Hu, N; Avit, G; Pristovsek, M; Honda, Y; Amano, H

APPLIED PHYSICS LETTERS Vol. 121 ( 8 ) 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We studied indium incorporation into InGaN/GaN quantum wells grown by metal-organic vapor phase epitaxy by systematically varying of gallium and indium precursor flows on (0001), (10 1 ¯3), (11 2 ¯2), and (10 1 ¯0) orientations. The layer thickness and indium composition obtained from x-ray diffraction analysis were correlated with a model based on indium and gallium incorporation efficiencies. In the model, the indium incorporation efficiency is reproduced by the Langmuir surface coverage of gallium, indicating that indium atoms close to gallium atoms can be incorporated preferably.

DOI： 10.1063/5.0088908

Surface kinetics in halide vapor phase epitaxial growth of GaN layers on GaN (0001) freestanding substrates Reviewed Open Access

Ohnishi, K; Fujimoto, N; Nitta, S; Watanabe, H; Honda, Y; Amano, H

JOURNAL OF CRYSTAL GROWTH Vol. 592 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth

The effects of halide vapor phase epitaxial (HVPE) growth conditions such as input V/III ratio and substrate off-cut angle on the surface morphology of n-type GaN layers grown on GaN (0001) freestanding substrates were investigated to develop a model for growing smooth surfaces. The spiral hillock density increased with increasing input V/III ratio and/or decreasing off-cut angle. The critical off-cut angle between the spiral growth and the step-flow growth depended on the vapor supersaturation calculated by thermodynamic analysis. To understand the transition of the growth mode, we proposed a Burton–Cabrera–Frank-theory-based model considering the effect of spiral growth, which was utilized to explain the obtained experimental results. The developed growth model can be effective for predicting the HVPE growth mode between the spiral growth and the step-flow growth.

DOI： 10.1016/j.jcrysgro.2022.126749

Improved performance of deep ultraviolet AlGaN-based light-emitting diode by reducing contact resistance of Al-based reflector Reviewed

Sim K.B., Jin J.Y., Kim S.K., Ko Y.J., Hwang G.W., Seong T.Y., Amano H.

Journal of Alloys and Compounds Vol. 910 2022.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

In this study, chlorine (Cl) treatment was carried out on p-AlGaN to enhance the performance of ultraviolet-C light emitting diodes (UVC LEDs) by modifying ITO work function and hence reducing the contact resistance of ITO/Al reflector. The Cl-treated UVC LEDs exhibit the forward voltage of 6.88 V at 20 mA, whereas the reference samples show 7.50 V. The light output power and relative wall plug efficiency (WPE) of the Cl-treated UVC LEDs are enhanced by 17.1% at 500 mW and 19.5% at 100 mA, respectively, as compared to the reference. Additionally, the Cl-treated LEDs also display reduction in both the leakage current and ideality factor. Further, the photoluminescence (PL) intensity of AlGaN micro-disks is also enhanced by the Cl-treatment. X-ray photoemission spectroscopy (XPS) results indicate the formation of Cl-ITO at the ITO/p-AlGaN interface and the passivation of the surface states of AlGaN by Cl radicals. Based on the XPS results, a possible mechanism for the improved performance of Cl-treated UVC AlGaN-based LEDs is described and discussed.

DOI： 10.1016/j.jallcom.2022.164895

Weak metastability of Al x Ga1-x N (x=13/24, 15/24, 17/24) shown by analyzing AlGaN grown on AlN with dense macrosteps Reviewed

Hirano, A; Nagasawa, Y; Ippommatsu, M; Sako, H; Hashimoto, A; Sugie, R; Honda, Y; Amano, H; Kojima, K; Chichibu, SF

APPLIED PHYSICS EXPRESS Vol. 15 ( 7 ) 2022.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

Energy-dispersive X-ray signals calibrated by Rutherford backscattering indicated the generation of Al13/24Ga11/24N in Ga-rich stripes in a nonflat Al0.58Ga0.42N layer. Also, the CL peak wavelengths of ∼259 and 272 nm also showed the generation of Al15/24Ga9/24N and Al13/24Ga11/24N in Al-rich zones and Ga-rich stripes, respectively. The wavelength of a strong CL peak at ∼246 nm, which was observed from the Al0.7Ga0.3N layer in our previous study, is also considered to correspond to the near-band-emission wavelengths of Al17/24Ga7/24N. In particular, the stronger reproducibility of metastable Al15/24Ga9/24N generation was confirmed, in agreement with the computed predictions by other research groups.

DOI： 10.35848/1882-0786/ac79a1

Space-Charge Profiles and Carrier Transport Properties in Dopant-Free GaN-Based p-n Junction Formed by Distributed Polarization Doping Reviewed

Kumabe, T; Kawasaki, S; Watanabe, H; Nitta, S; Honda, Y; Amano, H

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS Vol. 16 ( 7 ) 2022.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi - Rapid Research Letters

Herein, the operation of dopant-free GaN-based p-n junctions formed by distributed polarization doping (DPD) is experimentally demonstrated and their space charge profiles and carrier transport properties are investigated. The device exhibits ideal space charge profiles explained by polarization effects and demonstrates the excellent controllability of DPD. In addition, it shows rectification and electroluminescence under forward-biased conditions. The carrier transport properties could be explained by the conventional recombination/diffusion model used for impurity-doped p-n junctions. Repeatable breakdowns are also observed in all devices and the temperature-dependent breakdown voltages reveal that the breakdowns are caused by avalanche multiplication, which is also the same as those reported in impurity-doped GaN p-n diodes. These results indicate that DPD is a promising doping technology for GaN-based power devices overcoming any issues associated with conventional impurity doping.

DOI： 10.1002/pssr.202200127

Dual-peak electroluminescence spectra generated from Al n /12Ga1-n/12N (n=2, 3, 4) for AlGaN-based LEDs with nonflat quantum wells Reviewed

Nagasawa, Y; Kojima, K; Hirano, A; Ippommatsu, M; Honda, Y; Amano, H; Chichibu, SF

JOURNAL OF PHYSICS D-APPLIED PHYSICS Vol. 55 ( 25 ) 2022.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics D: Applied Physics

The metastability of Al n/12Ga1-n/12N (n = 2, 3, and 4) was investigated by the statistical analysis of electroluminescence (EL) spectra having dual peaks with a peak-to-peak distance (pp) of >10 nm generated from nonflat Al x Ga1-x N (x ∼0.2) quantum wells (QWs) fabricated on c(0001) sapphire substrates with a miscut of 1.0° towards the m[1 1ˉ 00] axis. To explain the origins of the dual-peak EL (DPEL) spectra, which are often observed for AlGaN-QWs with Ga content of greater than 0.7, a nonflat QW model incorporating two metastable compositions, Al(n-1)/12Ga1-(n-1)/12N and Al n/12Ga1-n/12N (n: integer), is proposed. By the statistical analysis of peak wavelengths in DPEL spectra and the verification of EL spectral shapes, two series of featured EL peak wavelengths with intervals of 2-3 nm were obtained from five out of six LED wafers. The two series of featured EL peak wavelengths were assigned by comparison with the calculated EL wavelengths. Then, Al2/12Ga10/12N and Al3/12Ga9/12N were determined to be the origins of peaks with the longer and shorter wavelengths in the DPEL, respectively, in addition to the metastable Al n/12Ga1-n/12N (n= 4-9) compositions observed in our previous studies. When DPEL (pp> 10 nm) appeared, the difference in QW thickness between Al2/12Ga10/12N and Al3/12Ga9/12N tended to be larger than one monolayer (ML), indicating a significant amount of Ga or GaN mass transport. Furthermore, the Al2/12Ga10/12N and Al3/12Ga9/12N QWs are considered to have thicknesses of m ML (m: consecutive integers), suggesting the 1 ML configuration of Al and Ga atoms on the c(0001) plane. In addition, the DPEL obtained from nonflat Al x Ga1-x N (x ∼0.25) QWs by another research group was shown to be related to two metastable Al n/12Ga1-n/12N (n = 3, 4), similarly to our one exceptional LED wafer, which also agreed with the model proposed in this work.

DOI： 10.1088/1361-6463/ac5d03

Author Correction: Laser slice thinning of GaN-on-GaN high electron mobility transistors. Open Access

Tanaka A, Sugiura R, Kawaguchi D, Wani Y, Watanabe H, Sena H, Ando Y, Honda Y, Igasaki Y, Wakejima A, Ando Y, Amano H

Scientific reports Vol. 12 ( 1 ) page： 8175 2022.5

Interplay of sidewall damage and light extraction efficiency of micro-LEDs Reviewed

Park, JH; Pristovsek, M; Cai, WT; Cheong, H; Kumabe, T; Lee, DS; Seong, TY; Amano, H

OPTICS LETTERS Vol. 47 ( 9 ) page： 2250 - 2253 2022.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Optics Letters

This Letter describes the impact of shape on micro light-emitting diodes (µLEDs), analyzing 400 µm2 area µLEDs with various mesa shapes (circular, square, and stripes). Appropriate external quantum efficiency (EQE) can yield internal quantum efficiency (IQE) which decreases with increasing peripheral length of the mesas. However, light extraction efficiency (ηe) increased with increasing mesa periphery. We introduce analysis of Jpeak (the current at peak EQE) since it is proportional to the non-radiative recombination. Etching the sidewalls using tetramethylammonium hydroxide (TMAH) increased the peak EQE and decreased the sidewall dependency of Jpeak. Quantitatively, the TMAH etching reduced non-radiative surface recombination by a factor of four. Hence, shrinking µLEDs needs an understanding of the relationship between non-radiative recombination and ηe, where analyzing Jpeak can offer new insights.

DOI： 10.1364/OL.456993

The effect of dry etching condition on the performance of blue micro light-emitting diodes with reduced quantum confined Stark effect epitaxial layer Reviewed

Park Jeong-Hwan, Cai Wentao, Cheong Heajeong, Ushida Yasuhisa, Lee Da-Hoon, Ando Yuto, Furusawa Yuta, Honda Yoshio, Lee Dong-Seon, Seong Tae-Yeon, Amano Hiroshi

JOURNAL OF APPLIED PHYSICS Vol. 131 ( 15 ) 2022.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

As the size of micro light-emitting diodes (μLEDs) decreases, μLEDs encounter etching damage especially at the sidewalls that critically affects their properties. In this study, we investigated the influence of etching bias power (Pbias) on the performance of μLEDs and found that the current-voltage and light output-current characteristics of μLEDs were enhanced when Pbias was reduced. It was shown that at low Pbias, the chemical reaction between etching gas and gallium nitride, rather than ion sputtering, dominated the etching process, leading to low plasma damage and rough surface morphology. Additionally, to understand the etching-induced surface roughening behaviors, various substrates with different threading dislocation densities were treated at low Pbias. It was found that for the sample (with p-contact size of 10 × 10 μm2), the efficiency droop was approximately 20%, although the current reached 10 mA due most probably to the suppressed polarization effect in the quantum well. It was further observed that the external quantum efficiency (EQE) was dependent on Pbias, where the lowest Pbias yielded the highest maximum EQE, indicating that the plasma damage was mitigated by reducing Pbias. Optimization of dry etching and polarization-suppression conditions could pave the way for realizing high-performance and brightness μLEDs for next-generation displays.

DOI： 10.1063/5.0085384

"Regrowth-free" fabrication of high-current-gain AlGaN/GaN heterojunction bipolar transistor with N-p-n configuration Reviewed Open Access

Kumabe, T; Watanabe, H; Ando, Y; Tanaka, A; Nitta, S; Honda, Y; Amano, H

APPLIED PHYSICS EXPRESS Vol. 15 ( 4 ) 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

An AlGaN/GaN heterojunction bipolar transistor (HBT) with N-p-n configuration was fabricated by the "regrowth-free"method, resulting in a contamination-free emitter-base AlGaN/GaN heterojunction. The low-bias-power-based low-damage inductively coupled plasma-reactive ion etching was employed in this study for emitter mesa definition instead of the conventional selective-area-regrowth technique. The method successfully minimized the etching-induced damage in the p-GaN base layer and the contamination at the emitter-base AlGaN/GaN heterojunction. Consequently, the fabricated device exhibited a high current gain of 25, the highest current density of 15.0 kA cm-2, and the lowest on-state voltage offset of 0.75 V ever reported for AlGaN/GaN HBTs.

DOI： 10.35848/1882-0786/ac6197

Mechanism and enhancement of anti-parasitic-reaction catalytic activity of tungsten-carbide-coated graphite components for the growth of bulk GaN crystals Reviewed Open Access

Nakamura, D; Iida, K; Horibuchi, K; Aoki, Y; Takahashi, N; Mori, Y; Moriyama, M; Nitta, S; Amano, H

APPLIED PHYSICS EXPRESS Vol. 15 ( 4 ) 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

The working mechanism of the anti-parasitic-reaction (APR) catalyst of tungsten carbide (WC) coating on graphite in hydride vapor phase epitaxy GaN growth were examined. During NH3 annealing, the surface of WC is reduced as well as nitrided. The W2N topmost layer was found to work as an APR-active catalyst to suppress the formation of GaN polycrystals during high-rate HVPE-GaN growth, while the regions covered with thick pyrolytic graphite residues were catalytically inert. The formation of an additional W2C top layer on the WC underlayer was demonstrated to exhibit superior APR activity, i.e. complete suppression of GaN polycrystal formation.

DOI： 10.35848/1882-0786/ac5ba4

Sputtered polycrystalline MgZnO/Al reflective electrodes for enhanced light emission in AlGaN-based homojunction tunnel junction DUV-LED Reviewed Open Access

Matsubara, T; Nagatat, K; Kushimoto, M; Tomai, S; Katsumata, S; Honda, Y; Amano, H

APPLIED PHYSICS EXPRESS Vol. 15 ( 4 ) 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

In this study, we enhanced the emission power of AlGaN-based tunnel junction deep-ultraviolet LEDs (TJ LEDs) by using a MgZnO and aluminum stacked structure as UV reflective electrodes on the anode side. The emission wavelength of the fabricated TJ LED was 284 nm, and the emission power was 57.3 mW at 63 A cm-2. The polycrystalline MgZnO enabled both conductivity and UV transmittance to be achieved, approximately doubling with a reflectance of the fabricated TJ LED at 284 nm compared to conventional TJ LED with Ti/Al. These factors contributed to the increased emission power of TJ LEDs.

DOI： 10.35848/1882-0786/ac5acf

Structural design optimization of 279 nm wavelength AlGaN homojunction tunnel junction deep-UV light-emitting diode Reviewed Open Access

Nagata K., Anada S., Miwa H., Matsui S., Boyama S., Saito Y., Kushimoto M., Honda Y., Takeuchi T., Amano H.

Applied Physics Express Vol. 15 ( 4 ) 2022.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

We demonstrated the structural optimization of AlGaN tunnel junction (TJ) deep-ultraviolet light-emitting diodes by changing the thickness and impurity concentrations of p+-type and n+-type AlGaN constituting the TJ. By decreasing the total thickness of the TJ to 23 nm, the operating voltage reached a minimum of 8.8 V at 63 A cm-2. Further decrease in TJ thickness markedly increases the operating voltage. This finding implies that the depletion layer width becomes greater than the TJ thickness if it is smaller than 12 nm. Therefore, we conclude that the TJ thickness must be greater than the depletion layer width.

DOI： 10.35848/1882-0786/ac60c7

Improved device performance of vertical GaN-on-GaN nanorod Schottky barrier diodes with wet-etching process Reviewed Open Access

Liao Y., Chen T., Wang J., Cai W., Ando Y., Yang X., Watanabe H., Tanaka A., Nitta S., Honda Y., Chen K.J., Amano H.

Applied Physics Letters Vol. 120 ( 12 ) 2022.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

In this work, a deliberate etching-based top-down approach is proposed to fabricate the GaN nanorod (NR) Schottky barrier diode (SBD). As a key step during the fabrication, the impact of the wet-etching process on device performance is systematically studied. By virtue of the reduced surface states at the sidewall, the performance of NR SBD with the wet-etching process is substantially improved, delivering a forward turn-on voltage of 0.65 V, a current density of ∼10 kA/cm2 at 3 V, an ideality factor of 1.03, an ON/OFF current ratio of ∼1010, and no severe current collapse, along with a reverse breakdown voltage of 772 V.

DOI： 10.1063/5.0083194

Inhomogeneous Barrier Height Characteristics of n-Type AlInP for Red AlGaInP-Based Light-Emitting Diodes Reviewed

Cha, JS; Lee, DH; Sim, KB; Lee, TJ; Seong, TY; Amano, H

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 11 ( 3 ) 2022.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ECS Journal of Solid State Science and Technology

For micro-light-emitting diode (LED)-based display applications, such as virtual reality and augmented reality, high-performance Ohmic contacts (namely, the improvement of current injection efficiency) is vital to the realization of high-efficiency micro-LEDs. The surface Fermi level pinning characteristics could be comprehended in terms of the relation between work function of metals (M) and Schottky barrier height (SBH, B). In this study, we have investigated the surface Fermi level pinning characteristics of (001) n-AlInP surfaces by employing Schottky diodes with different metals. With an increase in the temperature, B increases linearly and ideality factors (n) decreases. This behavior is related to the barrier height inhomogeneity. Inhomogeneity-modelbased B is evaluated to be in the range of 0.86 1.30 eV, which is dependent on the metal work functions and are similar to those measured from capacitance-voltage relation. Further, The S-parameter, the relation between B and M (d B/d M), is 0.36. This is indicative of the partial pinning of the surface Fermi level at the surface states placed at 0.95 eV below the conduction band. Furthermore, it is also shown that (NH4)2S-passivation results in an increases the mean SBH and the S-parameter (e.g., 0.52).

DOI： 10.1149/2162-8777/ac5d66

Visualization of depletion layer in AlGaN homojunction p-n junction Reviewed Open Access

Nagata, K; Anada, S; Saito, Y; Kushimoto, M; Honda, Y; Takeuchi, T; Yamamoto, K; Hirayama, T; Amano, H

APPLIED PHYSICS EXPRESS Vol. 15 ( 3 ) 2022.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

We analyzed the p-n junction of an aluminum gallium nitride (AlGaN) homojunction tunnel junction (TJ) deep-ultraviolet light-emitting diode by phase-shifting electron holography. We clearly obtained a phase image reflecting the band alinement of the p-n homojunction and derived a depletion layer width of approximately 10 nm. In addition, the observed depletion layer width for the AlGaN TJ was in good agreement with the simulated one reflecting the diffusion profile of Mg and Si, thus enabling a discussion on the electrical conduction mechanism for an AlGaN p-n junction.

DOI： 10.35848/1882-0786/ac53e2

The photoemission characteristic of InGaN in NEA activation under heating

Kashima Masahiro, Itokawa Yuya, Kanai Toshiya, Sato Daiki, Koizumi Atsushi, Iijima Hokuto, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi, Meguro Takashi

JSAP Annual Meetings Extended Abstracts Vol. 2022.1 ( 0 ) page： 1343 - 1343 2022.2

Effect of beam current on defect formation by high-temperature implantation of Mg ions into GaN Reviewed Open Access

Itoh, Y; Watanabe, H; Ando, Y; Kano, E; Deki, M; Nitta, S; Honda, Y; Tanaka, A; Ikarashi, N; Amano, H

APPLIED PHYSICS EXPRESS Vol. 15 ( 2 ) 2022.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

We evaluated the beam current dependence of defect formation during Mg ion implantation into GaN at a high temperature of 1100 °C with two beam currents. Photoluminescence spectra suggest that low-beam-current implantation reduced the vacancy concentration and activated Mg to a greater extent. Moreover, scanning transmission electron microscopy analysis showed that low-beam-current implantation reduced the density of Mg segregation defects with inactive Mg and increased the density of intrinsic dislocation loops, suggesting decreases in the densities of Ga and N vacancies. The formation of these defects depended on beam current, which is an important parameter for defect suppression.

DOI： 10.35848/1882-0786/ac481b

Defect characterization of { 10 1 ¯ 3 } GaN by electron microscopy Reviewed Open Access

Kusch G., Frentrup M., Hu N., Amano H., Oliver R.A., Pristovsek M.

Journal of Applied Physics Vol. 131 ( 3 ) 2022.1

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

Advances in obtaining untwinned (10 1 ¯3)-oriented semi-polar GaN enable a new crystal orientation for the growth of green and red LED structures. We present a scanning electron microscopy study that combines the structural characterization of electron channeling contrast imaging with the optical characterization of cathodoluminescence hyperspectral imaging on a (10 1 ¯ 3) GaN layer. An extensive defect analysis revealed that the dominant defects consist of basal plane stacking faults (BSFs), prismatic stacking faults, partial dislocations, and threading dislocations. With a defect density of about an order of magnitude lower than in comparable. The optical properties of the defects have been characterized from 10 to 320 K, showing BSF luminescence at room temperature indicating a reduced density of non-radiative recombination centers in the as-grown samples compared to established semi- and non-polar orientations. Our findings suggest that growth along (10 1 ¯3) has the potential for higher radiative efficiency than established semi-polar orientations.

DOI： 10.1063/5.0077084

Perspective on thermal conductance across heterogeneously integrated interfaces for wide and ultrawide bandgap electronics Reviewed

Cheng, Z; Graham, S; Amano, H; Cahill, DG

APPLIED PHYSICS LETTERS Vol. 120 ( 3 ) 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Heterogeneous integration is important to create multi-functionality in future electronic devices. However, few thermal studies of the interfaces formed in these integrated devices have been reported before. Recently, integrated interfaces by surface-Activated bonding were found to have high thermal boundary conductance, which provides a solution for heat dissipation of GaN and β-Ga2O3-based power electronics. Here, we review the recent progress on the interfacial thermal transport across heterogeneously integrated interfaces, including transferred van der Waals force bonded interfaces, surface-Activated bonded interfaces, plasma bonded interfaces, and hydrophilic bonded interfaces. This Perspective specifically focuses on applications of thermal management strategies of electronics, especially power electronics. Finally, the challenges, such as high-Throughput thermal measurements of buried interfaces, thermal property-structure relations of interfaces bonded under different conditions, theoretical understanding of interfacial thermal transport, and device demonstrations, are pointed out.

DOI： 10.1063/5.0077039

Threshold increase and lasing inhibition due to hexagonal-pyramid-shaped hillocks in AlGaN-based DUV laser diodes on single-crystal AlN substrate Reviewed Open Access

Kushimoto, M; Zhang, ZY; Honda, Y; Schowalter, LJ; Sasaoka, C; Amano, H

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 61 ( 1 ) 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

The presence of hexagonal-pyramid-shaped hillocks (HPHs) in AlGaN epitaxial films affects device characteristics; this effect is significant in DUV laser diodes (LDs) on AlN substrates, where the presence of HPHs under the p-electrode increases the threshold current density and inhibits the lasing. In this study, we investigated the difference between the lasing characteristics of LDs with and without HPHs. It was found that in the presence of HPHs, the threshold excitation power density increased and the slope efficiency decreased by optical excitation. To investigate the cause of these phenomena, we performed structural, optical, and electrical analyses of the HPHs. Various imaging techniques were used to directly capture the characteristics of the HPHs. As a result, we concluded that HPHs cause the degradation of LD characteristics due to a combination of structural, optical, and electrical factors.

DOI： 10.35848/1347-4065/ac3a1d

Ohmic Contact to p-Type GaN Enabled by Post-Growth Diffusion of Magnesium Reviewed Open Access

Wang, J; Lu, S; Cai, WT; Kumabe, T; Ando, Y; Liao, YQ; Honda, Y; Xie, YH; Amano, H

IEEE ELECTRON DEVICE LETTERS Vol. 43 ( 1 ) page： 150 - 153 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Electron Device Letters

We demonstrated the formation of excellent Ohmic contact to p-type GaN (including the plasma etching-damaged p-type GaN which otherwise exhibited undetectable current within ±5 V) by the post-growth diffusion of magnesium. The specific contact resistivity on the order of 10-4Omega cm2 (extracted at V=0 V) was achieved on the plasma-damaged p-GaN with linear current-voltage characteristics by the transfer length method (TLM) measurement. The improvement in current by a factor of over 109 was also obtained on the plasma-damaged p-n junction diode after the same Mg-treatment. These experimental results indicate a great potential of post-growth diffusion of Mg to overcome the bottleneck of forming a good Ohmic contact to p-GaN.

DOI： 10.1109/LED.2021.3131057

Frontier electronics in memory of Professor Isamu Akasaki Invited

Amano, H

GALLIUM NITRIDE MATERIALS AND DEVICES XVII Vol. 12001 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

ISAMU AKASAKI, crystal grower, a pioneer of GaN-based blue light-emitting diodes (LEDs), and a Nobel Laureate in Physics, passed away because of pneumonia on April 1, 2021 at the age of 92. According to the Nobel Foundation, the LED lamp holds considerable promise for improving the quality of life of over 1.5 billion people worldwide who lack access to electricity grids. Owing to its low power requirements, it can be powered by cheap local solar energy. In this article, his pursuit of blue LEDs for 20 years is described.

DOI： 10.1117/12.2619005

An Accurate Approach to Develop Small Signal Circuit Models for AlGaN/GaN HEMTs Using Rational Functions and Dependent Current Sources Reviewed Open Access

Jadhav, A; Ozawa, T; Baratov, A; Asubar, JT; Kuzuhara, M; Wakejima, A; Yamashita, S; Deki, M; Nitta, S; Honda, Y; Amano, H; Roy, S; Sarkar, B

IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY Vol. 10 page： 797 - 807 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of the Electron Devices Society

In this paper, a technique to develop small signal circuit (SSC) models of AlGaN/GaN high electron mobility transistors (HEMTs) using dependent current sources is presented. In this technique, experimentally measured broadband Y-parameters of AlGaN/GaN HEMTs are mathematically modeled as a sum of pole-residue terms. By representing each pole-residue term as a dependent current source, it is possible to develop an accurate SSC models for HEMTs which otherwise may not be possible using passive resistive-inductive-capacitive elements. The accuracy of the proposed SSC model is validated against the conventional SSC model using a 2nd, 3rd and 4th order rational function representation of the admittance branches of AlGaN/GaN HEMTs. Therefore, the proposed SSC model turns out to be highly robust in nature and can take care of any form of the transfer functions of the admittance branches between the gate, drain, and source terminal of an AlGaN/GaN HEMT.

DOI： 10.1109/JEDS.2022.3208028

Promising Results of National Project by Japanese Ministry of the Environment to Develop GaN on GaN Power Devices and Prove their Usefulness in Real Systems

Otoki Y., Shibata M., Mishima T., Ohta H., Mori Y., Imanishi M., Tamura S., Kidera K., Takino J., Okayama Y., Watanabe K., Okamoto N., Honda Y., Yamamoto M., Shiozaki K., Amano H.

2022 International Conference on Compound Semiconductor Manufacturing Technology, CS MANTECH 2022 page： 237 - 242 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：2022 International Conference on Compound Semiconductor Manufacturing Technology, CS MANTECH 2022

Exciting high performance power electronic devices have been widely demonstrated and manufactured using GaN epitaxial layers, but the majority of these devices have been fabricated on lattice mismatched substrates, including SiC, Si, or sapphire. Unfortunately, using lattice mismatched substrates inevitably introduces high concentrations of point defects and dislocations into the GaN epilayers, and these defects degrade the electrical performance of the fabricated GaN devices. Also, the mismatch of lattice constant and coefficient of thermal expansion cause strain and wafer bowing in the GaN epi, which further degrade the quality material for device fabrication. Using lattice matched GaN substrates provides solutions to these problems. In 2014, the Ministry of the Environment launched a national project to develop the required technology and to prove the superiority of GaN on GaN devices in real systems, with more than 10 partnerships from academia and industry. The project included work in several areas, including GaN substrate growth, GaN epitaxy, material characterization, and fabrication of devices and ICs for application in various systems. Large area GaN substrates have been grown with low defect densities, which has enabled fabrication of new types of vertical and horizontal GaN devices. The GaN devices have been used in servers, solar cell power conditioners, microwave ICs, distribution transformers, electric vehicle power converters. The performance improvements were compared with conventional approaches in each case. An “ALL GaN vehicle” has also been demonstrated, in which GaN devices are used in all power components. In this talk, we will present these results which show the great potential of GaN on GaN devices in the industry.

Development of Desktop Air Curtain System to Block Aerosols in Exhaled Breath Open Access

TAKAMURE Kotaro, SAKAMOTO Yasuaki, YAGI Tetsuya, IWATANI Yasumasa, AMANO Hiroshi, UCHIYAMA Tomomi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2022 ( 0 ) page： S055-10 2022

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

A desktop-type air curtain device capable of being installed on a desk to protect healthcare workers from infectious diseases was developed. Pseudo-exhaled air containing aerosol particles emitted from a mannequin was blown toward the air curtain generated by the air curtain device. The aerosol blocking effect of the air curtain device was investigated using particle image velocimetry measurements. Air curtain flow was maintained inside the gate of the air curtain device. The aerosol particles approaching the air curtain device were observed to abruptly bend towards the suction port without passing through the gate, signifying that the aerosol particles were blocked by the air curtain flow.

DOI： 10.1299/jsmemecj.2022.s055-10

Collection and Inactivation Abilities of Virus Flowing in a Return Air Channel with a DUV- LED Open Access

TAKAMURE Kotaro, IWATANI Yasumasa, SAKAMOTO Yasuaki, YAGI Tetsuya, AMANO Hiroshi, UCHIYAMA Tomomi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2022 ( 0 ) page： S055-11 2022

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

A virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The flow characteristics of virus particles inside the virus inactivation unit were investigated using numerical simulations. The percentage of particles colliding on the inner wall of the virus inactivation unit is 56 %. Especially, many particles collide with the partition plates behind the sharp-turn parts.

DOI： 10.1299/jsmemecj.2022.s055-11

Uniting a III-Nitride Transmitter, Waveguide, Modulator, and Receiver on a Single Chip Reviewed

Blocking and collecting effect of aerosol particles by desktop air curtain system Open Access

TAKAMURE Kotaro, KOBAYASHI Daisuke, MUTO Hiromasa, HARUKI Taketo, AMANO Hiroshi, YAGI Tetsuya, IWATANI Yasumasa, UCHIYAMA Tomomi

The Proceedings of the Fluids engineering conference Vol. 2022 ( 0 ) page： OS03-22 2022

Xie, MY; Jiang, Y; Gao, XM; Cai, W; Yuan, JL; Zhu, HB; Wang, YJ; Zeng, XF; Zhang, ZY; Liu, YH; Amano, H

ADVANCED ENGINEERING MATERIALS Vol. 23 ( 12 ) 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Advanced Engineering Materials

The integration of III-nitride electronics and photonics is of great interest toward future computing systems with low power consumption. Multifunctioning multiple quantum well (MQW) diodes can address the challenging issue for on-chip integration of a light source, which is a key component to drive the photonic circuits. Herein, a transmitter, waveguide, modulator, and receiver are monolithically integrated on a III-nitride-on-silicon platform to perform light emission, transmission, modulation, and detection simultaneously. Both the receiver and modulator exhibit sufficient sensitivity to optical signals from the transmitter, which has an identical InGaN/AlGaN multiple quantum well (MQW) structure because the III-nitride diode provides spectral overlap between the emission and absorption spectra. On-chip data communication among these optical components is achieved using light, and the effective wavelength range is from 365 to 385 nm, in which multifunctional devices can be operated.

DOI： 10.1002/adem.202100582

Discrete wavelengths observed in electroluminescence originating from Al<inf>1/2</inf>Ga<inf>1/2</inf>N and Al<inf>1/3</inf>Ga<inf>2/3</inf>N created in nonflat AlGaN quantum wells Reviewed

Nagasawa Y., Kojima K., Hirano A., Sako H., Hashimoto A., Sugie R., Ippommatsu M., Honda Y., Amano H., Chichibu S.F.

Journal of Physics D: Applied Physics Vol. 54 ( 48 ) 2021.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Physics D: Applied Physics

When nonflat Al x Ga1-x N quantum wells (QWs) for producing 285 nm light emitting diodes (LEDs) were fabricated on n-AlGaN on AlN templates with dense macrosteps on c(0001) sapphire substrates with a 1.0 miscut relative to the m[1-100] axis, composite electroluminescence (EL) spectra from both inclined and terrace zones in Al x Ga1-x N QWs (x∼ 1/3) were generated owing to compositional and thickness modulations. The shoulder or main peaks in composite EL spectra tended to locate at fixed discrete wavelengths of ∼287, ∼292, and ∼296 nm from 12 nonuniform 285 nm LED wafers that were involved in nonnegligible run-to-run drift, even though these wafers were fabricated using the same source gas flow parameters for metal-organic vapor phase epitaxy. The discrete wavelengths of ∼287, ∼292, and ∼296 nm were attributed to EL from Al1/3Ga2/3N QWs with thicknesses of 8, 9, and 10 monolayers (ML), respectively, by referring to the results of cathodoluminescence (CL) analysis. Also, when nonflat Al x Ga1-x N QWs (x∼ 1/2) for 265 nm LEDs were grown, single-peak-like EL spectra were mainly generated from the inclined zones in nonflat QWs. The EL spectra taken from four nonuniform 265 nm LED wafers tended to show weak structures or main peaks at ∼257, ∼261, ∼266, and ∼271 nm, which were also attributed to emissions from Al1/2Ga1/2N QWs with thicknesses of 5, 6, 7, and 8 ML, respectively, by referring to CL analysis results. The creation of Al1/3Ga2/3N and Al1/2Ga1/2N in nonflat QWs in this work was in agreement with the results of our previous studies that indicated the creation of metastable Al n/12Ga1-n/12N (n: consecutive natural numbers). Furthermore, QW thicknesses of consecutive n ML may imply that Al1/3Ga2/3N and Al1/2Ga1/2N have 1 ML configurations of Al and Ga atoms on a c(0001) plane.

DOI： 10.1088/1361-6463/ac2065

Multiple electron beam generation from InGaN photocathode Reviewed

Sato Daiki, Shikano Haruka, Koizumi Atsushi, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Vol. 39 ( 6 ) 2021.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics

In this study, we generated 25 multielectron beam (MEB) using an InGaN photocathode with a negative electron affinity state irradiating with 25 multilaser beam. The uniformity of the MEB and the total electron beam current were evaluated. A laser beam was split into 25 laser beams using a spatial light modulator. The coefficient of variation (CV) of laser power was 20%. The CV of quantum efficiency was 1.1%. The CV of electron beam current was 12%, and the total current was about 1.2 μA. These results will enhance the development of the MEB-defect inspection using the InGaN photocathode.

DOI： 10.1116/6.0001272

Modified Small Signal Circuit of AlGaN/GaN MOS-HEMTs Using Rational Functions Reviewed

Jadhav, A; Ozawa, T; Baratov, A; Asubar, JT; Kuzuhara, M; Wakejima, A; Yamashita, S; Deki, M; Nitta, S; Honda, Y; Amano, H; Roy, S; Sarkar, B

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 68 ( 12 ) page： 6059 - 6064 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

Conventional lumped small signal circuit (SSC) models of AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOS-HEMTs) are derived from the low frequency portion of the experimentally measured ${Y}$ -parameters. Consequently, these models cannot faithfully capture the high frequency behavior of the device. In this work, modified SSC models of AlGaN/GaN MOS-HEMTs are developed by fitting the entire broadband measured ${Y}$ -parameters of the device with rational functions. These rational functions are then physically realized using additional passive circuit elements added to the conventional SSC model. The accuracy of the proposed SSC models can be improved by increasing the order of the rational functions. The proposed models are demonstrably more accurate than the conventional SSC models in estimating the higher order poles and zeroes present in the experimentally measured ${Y}$ -parameters of AlGaN/GaN MOS-HEMTs.

DOI： 10.1109/TED.2021.3119528

Vertical GaN p+-n junction diode with ideal avalanche capability grown by halide vapor phase epitaxy (vol 119, 152102, 2021) Reviewed Open Access

Ohnishi, K; Kawasaki, S; Fujimoto, N; Nitta, S; Watanabe, H; Honda, Y; Amano, H

APPLIED PHYSICS LETTERS Vol. 119 ( 20 ) 2021.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

After the paper was published,1we found errors in the manuscript shown in page 152102-2. In the original published article, the SIMS detec-tion limits of [O] and [H] were written as 7 × 1015and 3 × 1015cm-3, respectively. The corrected detection limits of [O] and [H] are 6 × 1015and 3 × 1016cm-3, respectively. The SIMS depth profiles shown in Fig. 2(b) and the conclusions of the paper are not affected by this erratum.

DOI： 10.1063/5.0077364

OBITUARY Isamu Akasaki Reviewed

Amano, H

PHYSICS TODAY Vol. 74 ( 11 ) page： 63 - 63 2021.11

Vertical GaN p+-n junction diode with ideal avalanche capability grown by halide vapor phase epitaxy Reviewed Open Access

Ohnishi, K; Kawasaki, S; Fujimoto, N; Nitta, S; Watanabe, H; Honda, Y; Amano, H

APPLIED PHYSICS LETTERS Vol. 119 ( 15 ) 2021.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

A vertical GaN p+-n junction diode with an ideal breakdown voltage was grown by halide vapor phase epitaxy (HVPE). A steep p+-n interface was observed even with the use of the HVPE method. No Si-accumulating layer was formed at the p+-n interface because of the continuous HVPE growth from the n-type drift layer to the p-type layer. This method provides improved electrical properties compared with the regrowth of p-type GaN layers. The minimum ideality factor of approximately 1.6 was obtained. The breakdown voltage increased from 874 to 974 V with the increase in the temperature from 25 to 200 °C, which suggests that avalanche multiplication causes the breakdown. The temperature-dependent breakdown voltage was in good agreement with the breakdown voltage calculated using the ideal critical electric field. These results indicate that HVPE is promising for the fabrication of vertical GaN power devices.

DOI： 10.1063/5.0066139

Effective neutron detection using vertical-type BGaN diodes Reviewed

Nakano, T; Mochizuki, K; Arikawa, T; Nakagawa, H; Usami, S; Honda, Y; Amano, H; Vogt, A; Schuett, S; Fiederle, M; Kojima, K; Chichibu, SF; Inoue, Y; Aoki, T

JOURNAL OF APPLIED PHYSICS Vol. 130 ( 12 ) 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

In this study, vertical-type thick BGaN PIN diodes were successfully fabricated to improve the neutron capture rate of BGaN diodes by improving the BGaN epitaxial growth technique. In this technique, 5-μm-thick epitaxial growth was achieved using trimethylboron as a B metal-organic source, which suppressed the gas-phase reaction. The α-particle energy spectrum, the neutron pulse signal, and the residual energy of particles emitted from a neutron capture reaction were measured using the fabricated BGaN diodes by performing radiation detection measurements. The detected signal position in the neutron detection signal spectrum was similar to that of 2.3 MeV α-particles. These results indicate that vertical-type BGaN diodes can be used as effective neutron detectors.

DOI： 10.1063/5.0051053

Effects of Current, Temperature, and Chip Size on the Performance of AlGaInP-Based Red Micro-Light-Emitting Diodes with Different Contact Schemes

Lee, DH; Lee, SY; Shim, JI; Seong, TY; Amano, H

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 10 ( 9 ) 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ECS Journal of Solid State Science and Technology

We have investigated the performance of AlGaInP-based red micro-light-emitting diodes (micro-LEDs) with different n-type contact schemes as functions of current, ambient temperature, and chip size. The samples with AuGe/Ni/Au contact revealed wider full width at half maximum of electroluminescence than that with the Pd/Ge contact. All samples also exhibited broad peaks at wavelengths between ∼632 and ∼640 nm, whose intensity depended on the type of contact schemes and temperature. Regardless of the contact schemes, the 10 μm-size samples showed a larger temperature-dependent reduction in the output power at current density of <50 A cm-2 than the 100 μm-size ones. Above 100 A cm-2, however, both samples showed similar temperature dependence. Irrespective of the contact schemes, the main peak of the 100-μm samples was red-shifted, whereas no red-shift was detected in the 10-μm samples. The third peak of the AuGe-based contact samples became more dominant at 700 A cm-2 than the main peak, whereas that of the PdGe contact samples became more dominant at 1000 A cm-2. Based on the chip size, current, contact scheme, and temperature dependence, the performance degradation of the red micro-LEDs is described and discussed.

DOI： 10.1149/2162-8777/ac2029

Quasi-ballistic thermal conduction in 6H-SiC Reviewed Open Access

Cheng, Z; Lu, W; Shi, J; Tanaka, D; Protik, NH; Wang, S; Iwaya, M; Takeuchi, T; Kamiyama, S; Akasaki, I; Amano, H; Graham, S

MATERIALS TODAY PHYSICS Vol. 20 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Today Physics

The minimization of electronics makes heat dissipation of related devices an increasing challenge. When the size of materials is smaller than the phonon mean free paths, phonons transport without internal scattering and laws of diffusive thermal conduction need to be revisited. This work reports the temperature dependent thermal conductivity of doped epitaxial 6H–SiC and monocrystalline porous 6H–SiC below room temperature probed by time-domain thermoreflectance. Strong quasi-ballistic thermal transport was observed in these samples, especially at low temperatures. Doping and structural boundaries were applied to tune the quasi-ballistic thermal transport since dopants selectively scatter high-frequency phonons while boundaries scatter phonons with long mean free paths. Exceptionally strong phonon scattering by boron dopants are observed, compared to nitrogen dopants. Furthermore, orders of magnitude reduction in the measured thermal conductivity was observed at low temperatures for the porous 6H–SiC compared to the epitaxial 6H–SiC. Finally, first principles calculations and a simple Callaway model are built to understand the measured thermal conductivities. Our work sheds light on the fundamental understanding of thermal conduction in technologically-important wide bandgap semiconductors such as 6H–SiC and will impact applications such as thermal management of 6H–SiC-related electronics and devices.

DOI： 10.1016/j.mtphys.2021.100462

Gallium nitride wafer slicing by a sub-nanosecond laser: effect of pulse energy and laser shot spacing Reviewed Open Access

Sena, H; Tanaka, A; Wani, Y; Aratani, T; Yui, T; Kawaguchi, D; Sugiura, R; Honda, Y; Igasaki, Y; Amano, H

APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING Vol. 127 ( 9 ) 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics A: Materials Science and Processing

Gallium nitride (GaN)-based devices surpass the traditional silicon-based power devices in terms of higher breakdown voltage, faster-switching speed, higher thermal conductivity, and lower on-resistance. However, heteroepitaxial GaN growths like GaN on sapphire are not suitable for power devices due to the threading dislocation densities as high as 108/cm2. Recently, homoepitaxial GaN growth has become possible thanks to the native GaN substrates with dislocation densities in the order of 104/cm2 but the extremely high cost of the GaN substrates makes the homoepitaxy method unacceptable for industrial applications, and the slicing of wafers for reusing them is an effective solution for cost reduction. In this study, we will investigate a route for slicing the GaN single crystal substrate by controlling the laser pulse energy and changing the distance between each laser shot. The 2D and 3D crack propagations are observed by a multiphoton confocal microscope, and the cross section of samples is observed by a scanning electron microscope (SEM). The results showed that two types of radial and lateral cracking occurred depending on the pulse energy and shot pitch, and controlling them was of importance for attaining a smooth GaN substrate slicing. Cross-sectional SEM images showed that at suitable pulse energy and distance, crack propagation could be controlled with respect to the irradiation plane.

DOI： 10.1007/s00339-021-04808-y

High-Gain Gated Lateral Power Bipolar Junction Transistor Reviewed Open Access

Wang, J; Xie, YH; Amano, H

IEEE ELECTRON DEVICE LETTERS Vol. 42 ( 9 ) page： 1370 - 1373 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Electron Device Letters

We demonstrated a prototype Gated Lateral power bipolar junction transistor (GLP-BJT) on wide bandgap semiconductor. The device combined the intrinsic advantages of high current gain of a Gated Lateral-BJT and good current handling and voltage blocking capabilities of GaN material. As a result, the common-emitter current gain remained over 300 at a high collector current density of 2 kA/cm2 despite a wide p-base region of 2 μm. The open base breakdown voltage BVCEO was over 300 V corresponding to a high critical field of 2.5 MV/cm. These figures of merit show great promise of GaN-based GLP-BJT in power applications and also shed light on the development of state-of-the-art bipolar transistors based on other wide bandgap semiconductors.

DOI： 10.1109/LED.2021.3099982

Stable electrical performance of AlGaInP-based red micro-light emitting diode by controlling interfacial morphologies of metal contacts

Lee D.H., Seong Tae-Yeon, Amano Hiroshi

Journal of Alloys and Compounds Vol. 872 page： 159629 2021.8

Improving light output power of AlGaN-based deep-ultraviolet light-emitting diodes by optimizing the optical thickness of p-layers

Matsukura, Y; Inazu, T; Pernot, C; Shibata, N; Kushimoto, M; Deki, M; Honda, Y; Amano, H

APPLIED PHYSICS EXPRESS Vol. 14 ( 8 ) 2021.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

In this study, we investigated the relationship of light output power with the optical thickness of the p-layers in AlGaN-based deep ultraviolet light-emitting diodes with a transparent high-Al-composition p-AlGaN clad layer, a thin p-GaN contact layer, and a reflective p-type electrode. By adjusting the thickness of the transparent high-Al-composition p-AlGaN clad layer, we observed a marked change in light output power. A maximum light output power of 385 mW at 1500 mA, a maximum external quantum efficiency of 15.7% at 10 mA, and a maximum wall-plug efficiency of 15.3% at 10 mA were obtained at an emission wavelength of 275 nm.

DOI： 10.35848/1882-0786/ac154c

Reduction in operating voltage of AlGaN homojunction tunnel junction deep-UV light-emitting diodes by controlling impurity concentrations Open Access

Nagata K., Makino H., Miwa H., Matsui S., Boyama S., Saito Y., Kushimoto M., Honda Y., Takeuchi T., Amano H.

Applied Physics Express Vol. 14 ( 8 ) 2021.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

We reduced the operating voltage of AlGaN homojunction tunnel junction (TJ) deep-ultraviolet (UV) light-emitting diodes (LEDs) by two approaches: the suppression of carbon incorporation and the doping of a high concentration of silicon in an n+-AlGaN layer. The AlGaN homojunction TJ deep-UV LEDs had a significantly reduced forward voltage upon suppressing the incorporation of carbon in the n+-AlGaN layer. The suppression of electron compensation by carbon in nitrogen sites and the doping of a high concentration of silicon in an n+-AlGaN layer are important for reducing the operating voltage of AlGaN homojunction TJ deep-UV LEDs.

DOI： 10.35848/1882-0786/ac0fb6

Impact of gate electrode formation process on Al<inf>2</inf>O<inf>3</inf>/GaN interface properties and channel mobility

Ando Y., Deki M., Watanabe H., Taoka N., Tanaka A., Nitta S., Honda Y., Yamada H., Shimizu M., Nakamura T., Amano H.

Applied Physics Express Vol. 14 ( 8 ) 2021.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

The interface properties of GaN metal-insulator-semiconductor (MIS) structures with a gate electrode metal deposited by electron beam (EB) or resistive heating evaporation were investigated. Also, the impact of the interface properties on the channel mobility in GaN MIS field-effect transistors was investigated. It was confirmed that interface charges including both interface states and positive fixed charges were introduced to an Al2O3/GaN interface by the formation of a gate electrode by EB evaporation. Consequently, the introduced interface charges degraded the electron mobility in the MIS channel.

DOI： 10.35848/1882-0786/ac0ffa

Electrical properties and structural defects of p-type GaN layers grown by halide vapor phase epitaxy

Ohnishi, K; Amano, Y; Fujimoto, N; Nitta, S; Watanabe, H; Honda, Y; Amano, H

JOURNAL OF CRYSTAL GROWTH Vol. 566 2021.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth

The electrical properties and structural defects of p-type GaN layers with Mg concentrations from 8.0 × 1018 to 8.3 × 1019 cm−3 grown by halide vapor phase epitaxy (HVPE) were investigated. In all samples, p-type conduction was confirmed at room temperature. The hole concentration at room temperature decreased in a heavily Mg-doped sample. By analyzing the results of Hall-effect measurements at various temperatures, the acceptor concentration decreased in a heavily Mg-doped sample, whereas the compensating donor concentration increased. These results affect the decrease in the hole concentration. The hole mobility decreased with increasing acceptor concentration. In the heavily Mg-doped sample, pyramidal inversion domains (PIDs) were formed. The size of each PID in an HVPE-grown sample is in good agreement with that Mg-doped GaN layers grown by metalorganic vapor phase epitaxy (MOVPE). Thus, the formation mechanism of PIDs in HVPE-grown samples is possibly the same as that in MOVPE-grown samples. Energy-dispersive X-ray spectroscopy shows that Mg atoms accumulate in PIDs, which suggests that Mg atoms in PIDs are electrically inactive, inhibiting the increase in the acceptor concentration. These results are useful guidelines for fabricating p-type GaN layers with higher hole concentrations by HVPE.

DOI： 10.1016/j.jcrysgro.2021.126173

Vertical GaN-on-GaN nanowire Schottky barrier diodes by top-down fabrication approach

赤﨑勇先生のご逝去を悼む

天野浩

応用物理 Vol. 90 ( 7 ) page： 455 - 455 2021.7

赤﨑　勇先生を偲んで Open Access

天野浩

日本物理学会誌 Vol. 76 ( 7 ) page： 478 - 478 2021.7

Liao Y., Chen T., Wang J., Ando Y., Cai W., Yang X., Watanabe H., Hirotani J., Tanaka A., Nitta S., Honda Y., Chen K.J., Amano H.

Japanese Journal of Applied Physics Vol. 60 ( 7 ) 2021.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

An optimized top-down approach was utilized to fabricate vertical GaN-on-GaN nanowire Schottky barrier diodes (NWSBDs) in this letter. The suppressed reverse leakage current and enhanced breakdown voltage (BV) of the vertical GaN NWSBDs are attributed to the reduced electric field at the interface of the Schottky junction achieved through the dielectric reduced surface field technique. As-fabricated NWSBD delivers a low turn-on voltage of 0.80 V, a near-unity ideality factor of 1.04, along with a soft BV of 480 V. The measured soft BV is comparable with the avalanche BV of the p-n diode with a similar net doping concentration in the drift region.

DOI： 10.35848/1347-4065/ac06b5

Isamu Akasaki: The Pioneer of Blue LEDs and his Collaboration with pss OBITUARY Open Access

Amano, H

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 218 ( 14 ) 2021.7

Non-polar true-lateral GaN power diodes on foreign substrates Open Access

Wang, J; Yu, G; Zong, H; Liao, YQ; Lu, WF; Cai, WT; Hu, XD; Xie, YH; Amano, H

APPLIED PHYSICS LETTERS Vol. 118 ( 21 ) 2021.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We have demonstrated non-polar GaN power diodes (Schottky barrier diode and p-n junction diode) on foreign substrates featuring the true-lateral p-n and metal-semiconductor junctions. The diodes were fabricated on GaN islands laterally overgrown on the mask-patterned sapphire and Si substrates by metalorganic vapor phase epitaxy. The anode and cathode were formed on the opposed a-plane sidewalls of the island, making the device architecture essentially like the 90° rotation of the desired true-vertical power diodes. The ideality factor of the Schottky barrier diode remained 1.0 (from 1.00 to 1.05) over 7 decades in current. Specifically, a high critical electric field of 3.3 MV/cm was demonstrated on the p-n junction diode with avalanche capability. These performances reveal a strong potential of non-polar GaN with the true-lateral junctions for high power applications.

DOI： 10.1063/5.0051552

Etching-induced damage in heavily Mg-doped p-type GaN and its suppression by low-bias-power inductively coupled plasma-reactive ion etching Open Access

The stability of graphene and boron nitride for III-nitride epitaxy and post-growth exfoliation. Open Access

Park JH, Yang X, Lee JY, Park MD, Bae SY, Pristovsek M, Amano H, Lee DS

Chemical science Vol. 12 ( 22 ) page： 7713 - 7719 2021.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Science

A challenging approach, but one providing a key solution to material growth, remote epitaxy (RE)—a novel concept related to van der Waals epitaxy (vdWE)—requires the stability of a two-dimensional (2-D) material. However, when graphene, a representative 2-D material, is present on substrates that have a nitrogen atom, graphene loss occurs. Although this phenomenon has remained a hurdle for over a decade, restricting the advantages of applying graphene in the growth of III-nitride materials, few previous studies have been conducted. Here, we report the stability of graphene on substrates containing oxygen or nitrogen atoms. Graphene has been observed on highly decomposed Al2O3; however, graphene loss occurred on decomposed AlN at temperatures over 1300 °C. To overcome graphene loss, we investigated 2-D hexagonal boron nitride (h-BN) as an alternative. Unlike graphene on AlN, it was confirmed that h-BN on AlN was intact after the same high-temperature process. Moreover, the overgrown AlN layers on both h-BN/AlN and h-BN/Al2O3could be successfully exfoliated, which indicates that 2-D h-BN survived after AlN growth and underlines its availability for the vdWE/RE of III-nitrides with further mechanical transfer. By enhancing the stability of the 2-D material on the substrate, our study provides insights into the realization of a novel epitaxy concept.

DOI： 10.1039/d1sc01642c

Kumabe Takeru, Ando Yuto, Watanabe Hirotaka, Deki Manato, Tanaka Atsushi, Nitta Shugo, Honda Yoshio, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 60 ( SB ) page： SBBD03 2021.5

Impact of heat treatment process on threshold current density in AlGaN-based deep-ultraviolet laser diodes on AlN substrate Open Access

Kushimoto Maki, Zhang Ziyi, Sugiyama Naoharu, Honda Yoshio, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 14 ( 5 ) page： 051003 2021.5

Micro-Light Emitting Diode: From Chips to Applications

Parbrook Peter J., Corbett Brian, Han Jung, Seong Tae-Yeon, Amano Hiroshi

LASER & PHOTONICS REVIEWS Vol. 15 ( 5 ) page： 2000133 2021.5

Discrete AlN mole fraction of n/12 (n = 4-8) in Ga-rich zones functioning as electron pathways created in nonflat AlGaN layers grown on high-miscut sapphire substrates

Y. Nagasawa, A. Hirano, M. Ippommatsu, H. Sako, A. Hashimoto, R. Sugie, Y. Honda, H. Amano, I. Akasaki, K. Kojima, S. F. Chichibu

Journal of Applied Physics Vol. 129 ( 16 ) page： 164503 2021.4

Experimental demonstration of GaN IMPATT diode at X-band

Kawasaki Seiya, Ando Yuto, Deki Manato, Watanabe Hirotaka, Tanaka Atsushi, Nitta Shugo, Honda Yoshio, Arai Manabu, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 14 ( 4 ) page： 046501 2021.4

Optimization of Ni/Ag-Based Reflectors to Improve the Performance of 273 nm Deep Ultraviolet AlGaN-Based Light Emitting Diodes

Sim Kee-Baek, Kim Su-Kyung, Lee Hwa-Seub, Lee Sang-Youl, Seong Tae-Yeon, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 10 ( 4 ) page： 045005 2021.4

Numerical simulation of ammonothermal crystal growth of GaN-current state, challenges, and prospects Open Access

Crystals Vol. 11 ( 4 ) page： 356 2021.4

Strain-induced yellow to blue emission tailoring of axial InGaN/GaN quantum wells in GaN nanorods synthesized by nanoimprint lithography. Open Access

Avit G, Robin Y, Liao Y, Nan H, Pristovsek M, Amano H

Scientific reports Vol. 11 ( 1 ) page： 6754 2021.3

Progress in Modeling Compound Semiconductor Epitaxy: Unintentional Doping in GaN MOVPE

Kangawa Yoshihiro, Kusaba Akira, Kempisty Pawel, Shiraishi Kenji, Nitta Shugo, Amano Hiroshi

CRYSTAL GROWTH & DESIGN Vol. 21 ( 3 ) page： 1878 - 1890 2021.3

Fabrication of GaN cantilever on GaN substrate by photo-electrochemical etching

Yamada Takehiro, Ando Yuto, Watanabe Hirotaka, Furusawa Yuta, Tanaka Atsushi, Deki Manato, Nitta Shugo, Honda Yoshio, Suda Jun, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 14 ( 3 ) page： 036505 2021.3

Boundary Conditions for Simulations of Fluid Flow and Temperature Field during Ammonothermal Crystal Growth-A Machine-Learning Assisted Study of Autoclave Wall Temperature Distribution Open Access

Schimmel Saskia, Tomida Daisuke, Saito Makoto, Bao Quanxi, Ishiguro Toru, Honda Yoshio, Chichibu Shigefusa, Amano Hiroshi

CRYSTALS Vol. 11 ( 3 ) page： 1 - 27 2021.3

Development of Pulsed TEM Equipped with Nitride Semiconductor Photocathode for High-Speed Observation and Material Nanofabrication Open Access

Yasuda Hidehiro, Nishitani Tomohiro, Ichikawa Shuhei, Hatanaka Shuhei, Honda Yoshio, Amano Hiroshi

QUANTUM BEAM SCIENCE Vol. 5 ( 1 ) page： 5 2021.3

Suppression of the regrowth interface leakage current in AlGaN/GaN HEMTs by unactivated Mg doped GaN layer Open Access

Liu T., Watanabe H., Nitta S., Wang J., Yu G., Ando Y., Honda Y., Amano H., Tanaka A., Koide Y.

APPLIED PHYSICS LETTERS Vol. 118 ( 7 ) page： 072103 2021.2

Optical properties of neodymium ions in nanoscale regions of gallium nitride (vol 10, pg 2614, 2020) Open Access

Sato Shin-Ichiro, Deki Manato, Watanabe Hirotaka, Nitta Shugo, Honda Yoshio, Nishimura Tomoaki, Gibson Brant C., Greentree Andrew D., Amano Hiroshi, Ohshima Takeshi

OPTICAL MATERIALS EXPRESS Vol. 11 ( 2 ) page： 524 - 524 2021.2

3D GaN Power Switching Electronics: A Revival of Interest in ELO

Wang, J; Amano, H; Xie, YH

2021 5TH IEEE ELECTRON DEVICES TECHNOLOGY & MANUFACTURING CONFERENCE (EDTM) 2021

Language：English Publishing type：Research paper (scientific journal) Publisher：2021 5th IEEE Electron Devices Technology and Manufacturing Conference, EDTM 2021

We reported the first-time utilization of ELO (epitaxial lateral overgrowth) GaN (gallium nitride) for power diodes. The undesired stage of coalescence related to ELO is avoided by virtue of a novel 3D device architecture built on the ELO GaN islands on foreign substrate which features pure-lateral p-n and n+ -n-junctions and electrodes lying on the opposing sidewalls of the island. Excellent electrical performance was demonstrated, revealing a strong potential of ELO GaN with 3D device architecture for power switching applications.

DOI： 10.1109/EDTM50988.2021.9420859

Generalized Frequency Dependent Small Signal Model for High Frequency Analysis of AlGaN/GaN MOS-HEMTs Open Access

Jadhav A., Ozawa T., Baratov A., Asubar J.T., Kuzuhara M., Wakejima A., Yamashita S., Deki M., Honda Y., Roy S., Amano H., Sarkar B.

IEEE Journal of the Electron Devices Society Vol. 9 page： 570 - 581 2021

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of the Electron Devices Society

Traditional lumped small signal equivalent circuit models of AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOS-HEMTs) are made up of constant valued circuit elements. Such models are unable to capture the high frequency behavior (above 20 GHz) of the device. In this work, a modified small signal equivalent circuit model of AlGaN/GaN MOS-HEMTs is presented. The key feature of the proposed model is that the values of the different circuit elements in the model are considered to be frequency dependent in nature and not constants. The frequency dependent value of each circuit element is mathematically represented using polynomial functions where the coefficients of the functions are determined via a least-square curve fitting approach. This frequency dependent attribute of the circuit element values ensures that the proposed model is very accurate at high frequencies without sacrificing the compactness of the model topology. The accuracy of the proposed model has been verified up to 50 GHz using experimentally measured Y-parameters of AlGaN/GaN MOS-HEMTs having a different gate dielectric and gate length.

DOI： 10.1109/JEDS.2021.3081463

Development of UV-C laser diodes on AlN substrate

Kushimoto M.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 11686 2021

Decrease in the injection efficiency and generation of midgap states in UV-C LEDs: A model based on rate equations

Piva F.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 11686 2021

Electrical properties of GaN metal-insulator-semiconductor field-effect transistors with Al2O3/GaN interfaces formed on vicinal Ga-polar and nonpolar surfaces

Ando Yuto, Nagamatsu Kentaro, Deki Manato, Taoka Noriyuki, Tanaka Atsushi, Nitta Shugo, Honda Yoshio, Nakamura Tohru, Amano Hiroshi

APPLIED PHYSICS LETTERS Vol. 117 ( 24 ) page： 242104 2020.12

The 2020 UV emitter roadmap Open Access

Amano Hiroshi, Collazo Ramon, Santi Carlo De, Einfeldt Sven, Funato Mitsuru, Glaab Johannes, Hagedorn Sylvia, Hirano Akira, Hirayama Hideki, Ishii Ryota, Kashima Yukio, Kawakami Yoichi, Kirste Ronny, Kneissl Michael, Martin Robert, Mehnke Frank, Meneghini Matteo, Ougazzaden Abdallah, Parbrook Peter J., Rajan Siddharth, Reddy Pramod, Roemer Friedhard, Ruschel Jan, Sarkar Biplab, Scholz Ferdinand, Schowalter Leo J., Shields Philip, Sitar Zlatko, Sulmoni Luca, Wang Tao, Wernicke Tim, Weyers Markus, Witzigmann Bernd, Wu Yuh-Renn, Wunderer Thomas, Zhang Yuewei

Journal of Physics D: Applied Physics Vol. 53 ( 50 ) page： 503001 2020.12

Detailed analysis of Ga-rich current pathways created in an n-Al0.7Ga0.3N layer grown on an AlN template with dense macrosteps

Nagasawa Yosuke, Hirano Akira, Ippommatsu Masamichi, Sako Hideki, Hashimoto Ai, Sugie Ryuichi, Honda Yoshio, Amano Hiroshi, Akasaki Isamu, Kojima Kazunobu, Chichibu Shigefusa F.

Applied Physics Express Vol. 13 ( 12 ) page： 124001 2020.12

Surface passivation of light emitting diodes: From nano-size to conventional mesa-etched devices

Seong Tae-Yeon, Amano Hiroshi

SURFACES AND INTERFACES Vol. 21 page： 100765 2020.12

State-of-the-art and prospects for intense red radiation from core-shell InGaN/GaN nanorods Open Access

Evropeitsev Evgenii A., Kazanov Dmitrii R., Robin Yoann, Smirnov Alexander N., Eliseyev Ilya A., Davydov Valery Yu., Toropov Alexey A., Nitta Shugo, Shubina Tatiana V., Amano Hiroshi

SCIENTIFIC REPORTS Vol. 10 ( 1 ) page： 19048 2020.11

Limitation of simple np-n tunnel junction based LEDs grown by metal-organic vapor phase epitaxy Open Access

Robin Y., Bournet Q., Avit G., Pristovsek M., Andre Y., Trassoudaine A., Amano H.

SEMICONDUCTOR SCIENCE AND TECHNOLOGY Vol. 35 ( 11 ) page： 115005 2020.11

Modeling the degradation mechanisms of AlGaN-based UV-C LEDs: From injection efficiency to mid-gap state generation

PIVA F.

Photonics Research Vol. 8 ( 11 ) page： 1786 - 1791 2020.11

Epitaxial Combination of Two-Dimensional Hexagonal Boron Nitride with Single-Crystalline Diamond Substrate.

Yang X, Pristovsek M, Nitta S, Liu Y, Honda Y, Koide Y, Kawarada H, Amano H

ACS applied materials & interfaces Vol. 12 ( 41 ) page： 46466 - 46475 2020.10

Space charge profile study of AlGaN-based p-type distributed polarization doped claddings without impurity doping for UV-C laser diodes

Zhang Ziyi, Kushimoto Maki, Horita Masahiro, Sugiyama Naoharu, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

APPLIED PHYSICS LETTERS Vol. 117 ( 15 ) page： 152104 2020.10

Optical properties of neodymium ions in nanoscale regions of gallium nitride Open Access

Sato S.I.

Optical Materials Express Vol. 10 ( 10 ) page： 2614 - 2623 2020.10

Single-chip imaging system that simultaneously transmits light

Wang Yongjin, Gao Xumin, Fu Kang, Qin Feifei, Zhu Hongbo, Liu Yuhuai, Amano Hiroshi

Applied Physics Express Vol. 13 ( 10 ) 2020.10

High frequency GaN Devices for Realizing Wirelss Power Transmission System Invited Reviewed

Hiroshi Amano

J. IEICE Vol. 103 ( 10 ) page： 1016 - 1022 2020.10

Single-chip imaging system that simultaneously transmits light

Wang, YJ; Gao, XM; Fu, K; Qin, FF; Zhu, HB; Liu, YH; Amano, H

APPLIED PHYSICS EXPRESS Vol. 13 ( 10 ) 2020.10

Photoluminescence properties of implanted Praseodymium into Gallium Nitride at elevated temperatures

Sato S.i.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms Vol. 479 page： 7 - 12 2020.9

Low interface state densities at Al2O3/GaN interfaces formed on vicinal polar and non-polar surfaces Open Access

Ando Yuto, Nagamatsu Kentaro, Deki Manato, Taoka Noriyuki, Tanaka Atsushi, Nitta Shugo, Honda Yoshio, Nakamura Tohru, Amano Hiroshi

Applied Physics Letters Vol. 117 ( 10 ) page： 102012 2020.9

Design and characterization of a low-optical-loss UV-C laser diode

Zhang Ziyi, Kushimoto Maki, Sakai Tadayoshi, Sugiyama Naoharu, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

Japanese Journal of Applied Physics Vol. 59 ( 9 ) 2020.9

Design and characterization of a low-optical-loss UV-C laser diode

Zhang Ziyi, Kushimoto Maki, Sakai Tadayoshi, Sugiyama Naoharu, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 59 ( 9 ) 2020.9

Increasing the Luminescence Efficiency of Long-Wavelength (In,Ga)N Quantum Well Structures by Electric Field Engineering Using an (Al,Ga)N Capping Layer

Vichi Stefano, Robin Yoann, Sanguinetti Stefano, Pristovsek Markus, Amano Hiroshi

PHYSICAL REVIEW APPLIED Vol. 14 ( 2 ) page： 024018 2020.8

Thermodynamic analysis of the gas phase reaction of Mg-doped GaN growth by HVPE using MgO

Tomoya Kimura, Kazuki Ohnishi, Yuki Amano, Naoki Fujimoto, Masaaki Araidai, Shugo Nitta, Yoshio Honda, Hiroshi Amano, Yoshihiro Kangawa, Kenji Shiraish

Japanese Journal of Applied Physics Vol. 59 ( 8 ) page： 088001 2020.8

Growth of high-quality GaN by halogen-free vapor phase epitaxy

Kimura Taishi, Kataoka Keita, Uedono Akira, Amano Hiroshi, Nakamura Daisuke

Applied Physics Express Vol. 13 ( 8 ) page： 085509 2020.8

Thermodynamic analysis of the gas phase reaction of Mg-doped GaN growth by HVPE using MgO

Kimura Tomoya, Ohnishi Kazuki, Amano Yuki, Fujimoto Naoki, Araidai Masaaki, Nitta Shugo, Honda Yoshio, Amano Hiroshi, Kangawa Yoshihiro, Shiraishi Kenji

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 59 ( 8 ) 2020.8

Growth of high-quality GaN by halogen-free vapor phase epitaxy

Kimura Taishi, Kataoka Keita, Uedono Akira, Amano Hiroshi, Nakamura Daisuke

APPLIED PHYSICS EXPRESS Vol. 13 ( 8 ) 2020.8

Pulsed-flow growth of polar, semipolar and nonpolar AlGaN

Dinh Duc V, Hu Nan, Honda Yoshio, Amano Hiroshi, Pristovsek Markus

JOURNAL OF MATERIALS CHEMISTRY C Vol. 8 ( 25 ) page： 8668 - 8675 2020.7

Screw dislocation that converts p-type GaN to n-type: Microscopic study on Mg condensation and leakage current in p-n diodes Open Access

T. Nakano, Y. Harashima, K. Chokawa, K. Shiraishi, A. Oshiyama, Y. Kangawa, S. Usami, N. Mayama, K. Toda, A. Tanaka, Y. Honda, H. Amano

Applied Physics Letters Vol. 117 ( 1 ) page： 012105 2020.7

Change of high-voltage conduction mechanism in vertical GaN-on-GaN Schottky diodes at elevated temperatures

Abhinay Sandupatla, Subramaniam Arulkumaran, Geok Ing Ng, Kumud Ranjan, Manato Deki, Shugo Nitta, Yoshio Honda, Hiroshi Amano

Applied Physics Express Vol. 13 ( 7 ) page： 074001 2020.7

Change of high-voltage conduction mechanism in vertical GaN-on-GaN Schottky diodes at elevated temperatures

Sandupatla Abhinay, Arulkumaran Subramaniam, Ng Geok Ing, Ranjan Kumud, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 13 ( 7 ) 2020.7

Effect of Annealing on the Electrical and Optical Properties of MgZnO Films Deposited by Radio Frequency Magnetron Sputtering

Kushimoto Maki, Sakai Tadayoshi, Ueoka Yoshihiro, Tomai Shigekazu, Katsumata Satoshi, Deki Manato, Honda Yoshio, Amano Hiroshi

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 217 ( 14 ) page： 1900955 2020.7

Lattice bow in thick, homoepitaxial GaN layers for vertical power devices Open Access

Liu Qiang, Fujimoto Naoki, Shen Jian, Nitta Shugo, Tanaka Atsushi, Honda Yoshio, Sitar Zlatko, Bockowski Michal, Kumagai Yoshinao, Amano Hiroshi

Journal of Crystal Growth Vol. 539 page： 125643 2020.6

Halide vapor phase epitaxy of p-Type Mg-doped GaN utilizing MgO Open Access

Ohnishi Kazuki, Amano Yuki, Fujimoto Naoki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

Applied Physics Express Vol. 13 ( 6 ) page： 016007 2020.6

Halide vapor phase epitaxy of p-type Mg-doped GaN utilizing MgO Open Access

Ohnishi Kazuki, Amano Yuki, Fujimoto Naoki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 13 ( 6 ) 2020.6

Lattice bow in thick, homoepitaxial GaN layers for vertical power devices Open Access

Liu, Q; Fujimoto, N; Shen, J; Nitta, S; Tanaka, A; Honda, Y; Sitar, Z; Bockowski, M; Kumagai, Y; Amano, H

JOURNAL OF CRYSTAL GROWTH Vol. 539 2020.6

Oxygen Incorporation Kinetics in Vicinal m(10-10) Gallium Nitride Growth by Metal-Organic Vapor Phase Epitaxy

Yosho Daichi, Shintaku Fumiya, Inatomi Yuya, Kangawa Yoshihiro, Iwata Jun-Ichi, Oshiyama Atsushi, Shiraishi Kenji, Tanaka Atsushi, Amano Hiroshi

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS Vol. 14 ( 6 ) page： 2000142 2020.6

Vertical GaN-on-GaN Schottky Diodes as α-Particle Radiation Sensors. Open Access

Sandupatla A, Arulkumaran S, Ing NG, Nitta S, Kennedy J, Amano H

Micromachines Vol. 11 ( 5 ) page： 519 2020.5

Improving the Leakage Characteristics and Efficiency of GaN-based Micro-Light-Emitting Diode with Optimized Passivation

Lee Hoon, Lee Jung-Hoon, Park Jin-Seong, Seong Tae-Yeon, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 9 ( 5 ) page： 055001 2020.5

Impact of high-Temperature implantation of Mg ions into GaN Open Access

Takahashi Masahiro, Tanaka Atsushi, Ando Yuto, Watanabe Hirotaka, Deki Manato, Kushimoto Maki, Nitta Shugo, Honda Yoshio, Shima Kohei, Kojima Kazunobu, Chichibu Shigefusa F., Amano Hiroshi

Japanese Journal of Applied Physics Vol. 59 ( 5 ) page： 056502 2020.5

Computational study of oxygen stability in vicinal m(10-10)-GaN growth by MOVPE Open Access

Shintaku Fumiya, Yosho Daichi, Kangawa Yoshihiro, Iwata Jun-Ichi, Oshiyama Atsushi, Shiraishi Kenji, Tanaka Atsushi, Amano Hiroshi

Applied Physics Express Vol. 13 ( 5 ) page： 055507 2020.5

Impact of high-temperature implantation of Mg ions into GaN Open Access

Takahashi, M; Tanaka, A; Ando, Y; Watanabe, H; Deki, M; Kushimoto, M; Nitta, S; Honda, Y; Shima, K; Kojima, K; Chichibu, SF; Amano, H

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 59 ( 5 ) 2020.5

Computational study of oxygen stability in vicinal m(10-10)-GaN growth by MOVPE Open Access

Shintaku Fumiya, Yosho Daichi, Kangawa Yoshihiro, Iwata Jun-Ichi, Oshiyama Atsushi, Shiraishi Kenji, Tanaka Atsushi, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 13 ( 5 ) 2020.5

Improved Leakage and Output Characteristics of Pixelated LED Array for Headlight application

Lee Sang-Youl, Kang Kiman, Lee Eunduk, Jo Yoomin, Kim Doyub, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 9 ( 4 ) page： 045011 2020.4

Experimental observation of high intrinsic thermal conductivity of AlN Open Access

Cheng Zhe, Koh Yee Rui, Mamun Abdullah, Shi Jingjing, Bai Tingyu, Huynh Kenny, Yates Luke, Liu Zeyu, Li Ruiyang, Lee Eungkyu, Liao Michael E., Wang Yekan, Yu Hsuan Ming, Kushimoto Maki, Luo Tengfei, Goorsky Mark S., Hopkins Patrick E., Amano Hiroshi, Khan Asif, Graham Samuel

PHYSICAL REVIEW MATERIALS Vol. 4 ( 4 ) page： 044602 2020.4

Tungsten carbide layers deposited on graphite substrates via a wet powder process as anti-parasitic-reaction coatings for reactor components in GaN growth

Nakamura Daisuke, Kimura Taishi, Itoh Kenji, Fujimoto Naoki, Nitta Shugo, Amano Hiroshi

CRYSTENGCOMM Vol. 22 ( 15 ) page： 2632 - 2641 2020.4

Improved Light Output of AlGaInP-Based Micro-Light Emitting Diode Using Distributed Bragg Reflector

Lee Sang-Youl, Moon Ji Hyung, Moon Yong-Tae, Kim Chung Song, Park Sunwoo, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

IEEE PHOTONICS TECHNOLOGY LETTERS Vol. 32 ( 7 ) page： 438 - 441 2020.4

Scalable fabrication of GaN on amorphous substrates via MOCVD on highly oriented silicon seed layers

Hainey Mel Jr., Robin Yoann, Avit Geoffrey, Amano Hiroshi, Usami Noritaka

JOURNAL OF CRYSTAL GROWTH Vol. 535 page： 125522 2020.4

Demonstration of Observation of Dislocations in GaN by Novel Birefringence Method

Tanaka Atsushi, Inotsume Syo, Harada Shunta, Hanada Kenji, Honda Yoshio, Ujihara Toru, Amano Hiroshi

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS Vol. 257 ( 4 ) page： 1900553 2020.4

On-wafer fabrication of etched-mirror UV-C laser diodes with the ALD-deposited DBR Open Access

Sakai Tadayoshi, Kushimoto Maki, Zhang Ziyi, Sugiyama Naoharu, Schowalter Leo J., Honda Yoshio, Sasaoka Chiaki, Amano Hiroshi

APPLIED PHYSICS LETTERS Vol. 116 ( 12 ) page： 122101 2020.3

Effects of Ultraviolet Wavelength and Ambient Temperature on Reliability of Silicones in InAlGaN-Based Light-Emitting-Diode Package

Kim Ho-Young, Lee Jong-Woo, Jun Duk-Jin, Song Sung-Joo, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 9 ( 3 ) page： 035005 2020.3

Visualization of different carrier concentrations in n-type-GaN semiconductors by phase-shifting electron holography with multiple electron biprisms. Open Access

Yamamoto K, Nakano K, Tanaka A, Honda Y, Ando Y, Ogura M, Matsumoto M, Anada S, Ishikawa Y, Amano H, Hirayama T

Microscopy (Oxford, England) Vol. 69 ( 1 ) page： 1-10 2020.3

Using SiO2-Based Distributed Bragg Reflector to Improve the Performance of AlGaInP-Based Red Micro-Light Emitting Diode

Lee Sang-Youl, Moon Ji Hyung, Moon Yong-Tae, Choi Byoungjun, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 9 ( 3 ) page： 036002 2020.2

Using SiO<inf>2</inf>-based distributed Bragg reflector to improve the performance of AlGaInP-based red micro-light emitting diode

Lee S.Y., Moon J.H., Moon Y.T., Choi B., Oh J.T., Jeong H.H., Seong T.Y., Amano H.

ECS Journal of Solid State Science and Technology Vol. 9 ( 3 ) 2020.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ECS Journal of Solid State Science and Technology

We have investigated how different types of the reflectors affected the optical and electrical performance of AlGaInP-based micro-LEDs. Simulations showed that the AlGaAs-based epitaxial distributed Bragg reflector (DBR) had a stopband at the 610–624 nm region with reflectivity of 90%, the SiO2/TiO2 dielectric DBR gave a stopband at the 580–770 nm range with a maximum reflectivity of 99%, and the ITO/Ag metal reflector exhibited reflectivity of 90% across the 400–800 nm region. All micro-LEDs gave forward voltages of 1.895–1.960 V at 20 μA. The micro-LEDs with the dielectric DBR and metal reflector yielded 31% and 13% higher light output at 20 μA than that with the epitaxial DBR, respectively. All of the micro-LEDs contained a shoulder peak at approximately 615 nm in their electroluminescence spectra. Ray-tracing simulations exhibited that the micro-LEDs with the dielectric DBR and metal reflector produced 26% and 22% higher total light output power than the one with the epitaxial DBR, respectively. It was also shown that for the micro-LEDs with the metal reflector, some of the micro-LEDs were detached from the metal reflectors due to the interfacial voids induced as a result of agglomeration of Ag layer during fabrication process.

DOI： 10.1149/2162-8777/ab74c3/pdf

Optimization of InGaN thickness for high-quantum-efficiency Cs/O-activated InGaN photocathode

Sato Daiki, Honda Anna, Koizumi Atsushi, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi

MICROELECTRONIC ENGINEERING Vol. 223 page： 111229 2020.2

Effect of unevenly-distributed V pits on the optical and electrical characteristics of green micro-light emitting diode Open Access

Lee Da-Hoon, Kang Daesung, Seong Tae-Yeon, Kneissl Michael, Amano Hiroshi

JOURNAL OF PHYSICS D-APPLIED PHYSICS Vol. 53 ( 4 ) page： 045106 2020.1

Oblique-Angle Deposited SiO2/Al Omnidirectional Reflector for Enhancing the Performance of AlGaN-Based Ultraviolet Light-Emitting Diod

Jeongwon Lee, Tae-Yeon Seong, Hiroshi Amano

ECS Journal of Solid State Science and Technology Vol. 9 ( 2 ) 2020.1

Oblique-Angle Deposited SiO2/Al Omnidirectional Reflector for Enhancing the Performance of AlGaN-Based Ultraviolet Light-Emitting Diode

Jeongwon Lee, Tae-Yeon Seong, Hiroshi Amano

ECS Journal of Solid State Science and Technology Vol. 9 ( 2 ) page： 026005 2020.1

Heavy Mg Doping to Form Reliable Rh Reflective Ohmic Contact for 278 nm Deep Ultraviolet AlGaN-Based Light-Emitting Diodes

Lee Sang-Youl, Han Dae-Seob, Lee Yong-Gyeong, Choi Kwang-Ki, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 9 ( 6 ) page： 065016 2020.1

Improved breakdown voltage in vertical GaN Schottky barrier diodes on free-standing GaN with Mg-compensated drift layer

Abhinay S., Arulkumaran S., Ng G. I., Ranjan K., Deki M., Nitta S., Honda Y., Amano H.

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 59 ( 1 ) page： 010906 2020.1

Recovery of quantum efficiency on Cs/O-activated GaN and GaAs photocathodes by thermal annealing in vacuum Open Access

Daiki Sato, Tomohiro Nishitani, Yoshio Honda, Hiroshi Amano

Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics Vol. 38 ( 1 ) page： 012603 2020.1

Scalable synthesis of multilayer h-BN on AlN by metalorganic vapor phase epitaxy: nucleation and growth mechanism

Yang Xu, Nitta Shugo, Pristovsek Markus, Liu Yuhuai, Liao Yaqiang, Kushimoto Maki, Honda Yoshio, Amano Hiroshi

2D MATERIALS Vol. 7 ( 1 ) page： 015004 2020.1

Analysis of trimethylgallium decomposition by high-resolution mass spectrometry

Zheng Ye, Shugo Nitta, Yoshio Honda, Markus Pristovsek, Hiroshi Amano

Japanese Journal of Applied Physics Vol. 59 ( 2 ) page： 025511 2020

Indium incorporation and optical properties of polar, semipolar and nonpolar InAlN Open Access

Duc V Dinh, Nan Hu, Yoshio Honda, Hiroshi Amano, Markus Pristovsek

Semiconductor Science and Technology Vol. 35 ( 3 ) page： 035004 2020

Preface-JSS Focus Issue on Recent Advances inWide Bandgap III-Nitride Devices and Solid State Lighting: A Tribute to Isamu Akasaki

Ren Fan, Mishra Kailash C., Amano Hiroshi, Collins John, Han Jung, Im Won Bin, Kneissl Michael, Seong Tae-Yeon, Setlur Anant, Suski Tadek, Zych Eugeniusz

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 9 ( 1 ) page： 010001 2020

Damage-Free Plasma Etching to Enhance Performance of AlGaInP-Based Micro-Light Emitting Diode

Lee Sang-Youl, Lee Eunduk, Moon Ji-Hyung, Choi Byoungjun, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

IEEE PHOTONICS TECHNOLOGY LETTERS Vol. 32 ( 17 ) page： 1041 - 1044 2020

Characterization of AlGaN multiple-quantum-wells grown on c-plane AlN/sapphire templates with macro-steps

Kojima Kazunobu, Nagasawa Yosuke, Hirano Akira, Ippommatsu Masamichi, Sugie Ryuichi, Honda Yoshio, Amano Hiroshi, Akasaki Isamu, Chichibu Shigefusa F.

Journal of the Japanese Association for Crystal Growth Vol. 47 ( 3 ) page： n/a 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japanese Association for Crystal Growth

The microscopic structural and optical characteristics of AlGaN light-emitting diodes (LEDs) fabricated on the AlN templates with dense macrosteps are shown to clarify the origin of their high internal quantum efficiency of radiation (IQE). The cross-sectional transmission electron microscopy observations under the high-angle annular dark field scanning mode and microscopic energy dispersive X-ray spectroscopy revealed that the AlGaN cladding layer under the AlGaN quantum well (QW) layer had a microscopic compositional modulation, which originates from the macrosteps at the AlN template surface. Moreover, Ga-rich portions in the cladding layer behaved as current micropaths, and the micropaths are connected with the carrier localization structure formed in QWs. The in-plane cathodoluminescence (CL) spectroscopy showed a significant inhomogeneity of the CL characteristics. The gentle slopes at the sample surface showed brighter emissions with a lower peak photon energy, confirming the carrier localization. This carrier localization structure in the QWs combined with the current micropaths in the cladding layer can increase the IQE as well as external quantum efficiency of the AlGaN LEDs.

DOI： 10.19009/jjacg.47-3-04

Role of defects in the mid-term degradation of UV-B LEDs investigated by optical and DLTS measurements

Piva F., De Santi C., Deki M., Kushimoto M., Amano H., Tomozawa H., Shibata N., Meneghesso G., Zanoni E., Meneghini M.

GALLIUM NITRIDE MATERIALS AND DEVICES XV Vol. 11280 page： 1128015 2020

Low leakage Mg-compensated GaN Schottky diodes on free-standing GaN substrate for high energy alpha-particle detection

Sandupatia A., Arulkurnaran S., Ranjan K., Ng G. I, Murumu P. P., Kennedy J., Deki M., Nitta S., Honda Y., Amano H.

2020 IEEE ELECTRON DEVICES TECHNOLOGY AND MANUFACTURING CONFERENCE (EDTM 2020) 2020

Dielectric Ruduced Surface Field Effect on Vertical GaN-on-GaN Nanowire Schottky Barrier Diodes

PROCEEDINGS OF THE 2020 32ND INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES AND ICS (ISPSD 2020) Vol. 2020-September page： 349 - 352 2020

Development of laser slicing technology for GaN substrates Open Access

KAWAGUCHI Daisuke, TANAKA Atsushi, YUI Toshiki, IGASAKI Yasunori, WANI Yotaro, AMANO Hiroshi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2020 ( 0 ) page： S16306 2020

UV-C Laser Diodes Fabricated on High Quality AlN Substrate Open Access

SASAOKA Chiaki, AMANO Hiroshi

The Review of Laser Engineering Vol. 48 ( 8 ) page： 427 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Laser Society of Japan

A UV-C laser diode is a promising light source for processing and machining applications due to photon
energy near 5 eV. Recently, our group reported a 272-nm laser diode (LD) fabricated on a high-quality
AlN substrate. Several key technologies are involved to achieve lasing; a low-dislocation-density AlN
substrate to reduce waveguide optical loss, and distributed polarization doping to increase the hole density
in the p-side AlGaN cladding of high Al composition. After introducing these key technologies, we
describe a highly productive on-wafer laser fabrication process in which a facet mirror is prepared by
dry- and wet-etching and coated with atomic layer deposited DBR (Distributed Bragg Reflector). These
technologies are expected to open up new UV-C applications and be widely implemented around the
world.

DOI： 10.2184/lsj.48.8_427

Improvement of The Light Output of Blue InGaN-Based Light Emitting Diodes by Using a Buried Stripe -Type n-Contact and Reflective Bonding Pad Open Access

Kim Jong-Ho, Lee Yong Won, Im Hyeong-Seop, Oh Chan-Hyoung, Shim Jong-In, Kang Daesung, Seong Tae-Yeon, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 9 ( 1 ) page： 015021 2019.12

Two-dimensional analysis of the nonuniform quantum yields of multiple quantum wells for AlGaN-based deep-ultraviolet LEDs grown on AlN templates with dense macrosteps using cathodoluminescence spectroscopy

Nagasawa Yosuke, Sugie Ryuichi, Kojima Kazunobu, Hirano Akira, Ippommatsu Masamichi, Honda Yoshio, Amano Hiroshi, Akasaki Isamu, Chichibu Shigefusa F.

JOURNAL OF APPLIED PHYSICS Vol. 126 ( 21 ) page： 215703 2019.12

Suppression of Green Luminescence of Mg-Ion-Implanted GaN by Subsequent Implantation of Fluorine Ions at High Temperature

Takahashi Masahiro, Tanaka Atsushi, Ando Yuto, Watanabe Hirotaka, Deki Manato, Kushimoto Maki, Nitta Shugo, Honda Yoshio, Shima Kohei, Kojima Kazunobu, Chichibu Shigefusa F., Chen Kevin J., Amano Hiroshi

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS Vol. 257 page： 1900554 2019.12

A 271.8 nm deep-ultraviolet laser diode for room temperature operation Open Access

Zhang Ziyi, Kushimoto Maki, Sakai Tadayoshi, Sugiyama Naoharu, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 12 ( 12 ) page： 124003 2019.12

Untwinned semipolar (10(1)over-bar3) AlxGa1-xN layers grown on m-plane sapphire

Dinh Duc V., Hu Nan, Amano Hiroshi, Honda Yoshio, Pristovsek Markus

SEMICONDUCTOR SCIENCE AND TECHNOLOGY Vol. 34 ( 12 ) page： 125012 2019.12

Low Voltage High-Energy alpha-Particle Detectors by GaN-on-GaN Schottky Diodes with Record-High Charge Collection Efficiency Open Access

Sandupatla Abhinay, Arulkumaran Subramaniam, Ranjan Kumud, Ng Geok Ing, Murmu Peter P., Kennedy John, Nitta Shugo, Honda Yoshio, Deki Manato, Amano Hiroshi

SENSORS Vol. 19 ( 23 ) page： 5107 2019.12

Improvement in the Reliability of AlGaInP-Based Light-Emitting Diode Package Using Optimal Silicone and Leadframe Structure Open Access

Kim Ho-Young, Lee Jong Woo, Moon Young Min, Oh Jeong Tak, Jeong Hwan-Hee, Song June-O, Seong Tae-Yeon, Kneissl Michael, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 9 ( 1 ) page： 015014 2019.11

Aluminium incorporation in polar, semi- and non-polar AlGaN layers: a comparative study of x-ray diffraction and optical properties Open Access

Duc V Dinh, Hu Nan, Honda Yoshio, Amano Hiroshi, Pristovsek Markus

SCIENTIFIC REPORTS Vol. 9 page： 15802 2019.11

Hole injection mechanism in the quantum wells of blue light emitting diode with V pits for micro-display application

Kang Daesung, Oh Jeong-Tak, Song June-O, Seong Tae-Yeon, Kneissl Michael, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 12 ( 10 ) page： 102016 2019.10

V-shaped dislocations in a GaN epitaxial layer on GaN substrate Open Access

Tanaka Atsushi, Nagamatsu Kentaro, Usami Shigeyoshi, Kushimoto Maki, Deki Manato, Nitta Shugo, Honda Yoshio, Bockowski Michal, Amano Hiroshi

AIP ADVANCES Vol. 9 ( 9 ) page： 095002 2019.9

Stability and degradation of AlGaN-based UV-B LEDs: Role of doping and semiconductor defects

Piva F., De Santi C., Deki M., Kushimoto M., Amano H., Tomozawa H., Shibata N., Meneghesso G., Zanoni E., Meneghini M.

MICROELECTRONICS RELIABILITY Vol. 100 page： 113418 2019.9

Via-Hole-Type Flip-Chip Packaging to Improve the Thermal Characteristics and Reliability of Blue Light Emitting Diodes

Kim Ho Young, Lim Chang Man, Kim Ki Seok, Oh Jeong Tak, Jeong Hwan-Hee, Song June-O, Seong Tae-Yeon, Amano Hiroshi

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Vol. 8 ( 9 ) page： Q165 - Q170 2019.8

Combined effects of V pits and chip size on the electrical and optical properties of green InGaN-based light-emitting diodes

Kim Dae-Hyun, Park Young Soo, Kang Daesung, Kim Kyoung-Kook, Seong Tae-Yeon, Amano Hiroshi

JOURNAL OF ALLOYS AND COMPOUNDS Vol. 796 page： 146-152 2019.8

Indium Incorporation into InGaN Quantum Wells Grown on GaN Narrow Stripes Open Access

Sarzynski Marcin, Grzanka Ewa, Grzanka Szymon, Targowski Grzegorz, Czernecki Robert, Reszka Anna, Holy Vaclav, Nitta Shugo, Liu Zhibin, Amano Hiroshi, Leszczynski Mike

MATERIALS Vol. 12 ( 16 ) page： 2583 2019.8

Influence of Temperature-Dependent Substrate Decomposition on Graphene for Separable GaN Growth

Park Jeong-Hwan, Lee Jun-Yeob, Park Mun-Do, Min Jung-Hong, Lee Je-Sung, Yang Xu, Kang Seokjin, Kim Sang-Jo, Jeong Woo-Lim, Amano Hiroshi, Lee Dong-Seon

ADVANCED MATERIALS INTERFACES Vol. 6 page： 1900821 2019.7

Fabrication of a GaInN/GaInP/GaInAs/Ge four-junction solar cell using the wafer bonding technology

Takahashi Kazuya, Shinoda Ryoji, Mitsufuji Syun, Iwaya Motoaki, Kamiyama Satoshi, Takeuchi Tetsuya, Hattori Tomokazu, Akasaki Isamu, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( 7 ) page： 072003 2019.7

Origin of acceptor diffusion into silicon substrate during GaN growth by metal organic chemical vapor deposition Open Access

Matsumoto Koji, Ono Toshiaki, Honda Yoshio, Torigoe Kazuhisa, Kushimoto Maki, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( 7 ) page： 075502 2019.7

Ammonia decomposition and reaction by high-resolution mass spectrometry for group III - Nitride epitaxial growth Open Access

Ye Zheng, Nitta Shugo, Nagamatsu Kentaro, Fujimoto Naoki, Kushimoto Maki, Deki Manato, Tanaka Atsushi, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

JOURNAL OF CRYSTAL GROWTH Vol. 516 page： 63-66 2019.6

Direct evidence of Mg diffusion through threading mixed dislocations in GaN p-n diodes and its effect on reverse leakage current

Usami Shigeyoshi, Mayama Norihito, Toda Kazuya, Tanaka Atsushi, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

APPLIED PHYSICS LETTERS Vol. 114 ( 23 ) page： 232105 2019.6

Computational fluid dynamics simulation study of the gas flow balance in a vertical HVPE reactor with a showerhead for low cost bulk GaN crystal growth

Liu Qiang, Fujimoto Naoki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( SC ) page： SC1055 2019.6

Monolithic integration of tricolor micro-LEDs and color mixing investigation by analog and digital dimming Open Access

Robin Yoann, Hemeret Francois, D'Inca Gillian, Pristovsek Markus, Trassoudaine Agnes, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( SC ) page： SCCC06 2019.6

Effect of photoelectrochemical etching and post-metallization annealing on gate controllability of AlGaN/GaN high electron mobility transistors Open Access

Uemura Keisuke, Deki Manato, Honda Yoshio, Amano Hiroshi, Sato Taketomo

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( SC ) page： SCCD20 2019.6

Deeply and vertically etched butte structure of vertical GaN p-n diode with avalanche capability

Fukushima Hayata, Usami Shigeyoshi, Ogura Masaya, Ando Yuto, Tanaka Atsushi, Deki Manato, Kushimoto Maki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( SC ) page： SCCD25 2019.6

Correlation between nanopipes formed from screw dislocations during homoepitaxial growth by metal-organic vapor-phase epitaxy and reverse leakage current in vertical p-n diodes on a free-standing GaN substrates Open Access

Usami Shigeyoshi, Tanaka Atsushi, Fukushima Hayata, Ando Yuto, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( SC ) page： SCCB24 2019.6

Controlling the orientations of directional sputtered non- and semi-polar GaN/AlN layers

Nan Hu, Dinh Duc V., Pristovsek Markus, Honda Yoshio, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( SC ) page： SC1044 2019.6

Comparison of AlxGa1-xN multiple quantum wells designed for 265 and 285nm deep-ultraviolet LEDs grown on AlN templates having macrosteps

Nagasawa Yosuke, Kojima Kazunobu, Hirano Akira, Ipponmatsu Masamichi, Honda Yoshio, Amano Hiroshi, Akasaki Isamu, Chichibu Shigefusa F.

APPLIED PHYSICS EXPRESS Vol. 12 ( 6 ) page： 064009 2019.6

Narrow Excitonic Lines in Core-Shell Nanorods With InGaN/GaN Quantum Wells Intersected by Basal Stacking Faults

Evropeitsev Evgeniy A., Robin Yoann, Shubina Tatiana V., Bae Si-Young, Nitta Shugo, Kirilenko Demid A., Davydov Valery Y., Smirnov Alexandr N., Toropov Alexey A., Kushimoto Maki, Ivanov Sergey V., Amano Hiroshi

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS Vol. 256 ( 6 ) page： 1800648 2019.6

Morphological study of InGaN on GaN substrate by supersaturation (vol 508, pg 58, 2019)

Liu Zhibin, Nitta Shugo, Robin Yoann, Kushimoto Maki, Deki Manato, Honda Yoshio, Pristovsek Markus, Sitar Zlatko, Amano Hiroshi

JOURNAL OF CRYSTAL GROWTH Vol. 514 page： 13-13 2019.5

Effect of substrate misorientation on the concentration of impurities and surface morphology of an epitaxial GaN layer on N-polar GaN substrate by MOVPE Open Access

Nagamatsu Kentaro, Ando Yuto, Kono Tsukasa, Cheong Heajeong, Nitta Shugo, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

JOURNAL OF CRYSTAL GROWTH Vol. 512 page： 78-83 2019.4

Nonpolar m-plane AlxGa1-xN layers grown on m-plane sapphire by MOVPE Open Access

Duc V Dinh, Amano Hiroshi, Pristovsek Markus

JOURNAL OF CRYSTAL GROWTH Vol. 512 page： 100-104 2019.4

The emergence and prospects of deep-ultraviolet light-emitting diode technologies

Kneissl Michael, Seong Tae-Yeon, Han Jung, Amano Hiroshi

NATURE PHOTONICS Vol. 13 ( 4 ) page： 233-244 2019.4

GaN drift-layer thickness effects in vertical Schottky barrier diodes on free-standing HVPE GaN substrates Open Access

Sandupatla A., Arulkumaran S., Ng G. I., Ranjan K., Deki M., Nitta S., Honda Y., Amano H.

AIP ADVANCES Vol. 9 ( 4 ) page： 045007 2019.4

Transfer-free fabrication of a graphene transparent electrode on a GaN-based light-emitting diode using the direct precipitation method

Yamada Jumpei, Usami Shigeyoshi, Ueda Yuki, Honda Yoshio, Amano Hiroshi, Maruyama Takahiro, Naritsuka Shigeya

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( 4 ) page： 040904 2019.4

Effect of gas phase temperature on InGaN grown by metalorganic vapor phase epitaxy Open Access

Liu Zhibin, Nitta Shugo, Usami Shigeyoshi, Robin Yoann, Kushimoto Maki, Deki Manato, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

JOURNAL OF CRYSTAL GROWTH Vol. 509 page： 50-53 2019.3

GaN-on-Si resonant-cavity light-emitting diode incorporating top and bottom dielectric distributed Bragg reflectors Open Access

Cai Wei, Yuan Jialei, Ni Shuyu, Shi Zheng, Zhou Weidong, Liu Yuhuai, Wang Yongjin, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 12 ( 3 ) page： 032004 2019.3

Fully Ion Implanted Normally-Off GaN DMOSFETs with ALD-Al2O3 Gate Dielectrics Open Access

Yoshino Michitaka, Ando Yuto, Deki Manato, Toyabe Toru, Kuriyama Kazuo, Honda Yoshio, Nishimura Tomoaki, Amano Hiroshi, Kachi Tetsu, Nakamura Tohru

MATERIALS Vol. 12 ( 5 ) page： 689 2019.3

Effects of Drift Layer Thicknesses in Reverse Conduction Mechanism on Vertical GaN-on-GaN SBDs grown by MOCVD

Abhinay S., Arulkumaran S., Ng G.I., Ranjan K., Deki M., Nitta S., Honda Y., Amano H.

2019 Electron Devices Technology and Manufacturing Conference, EDTM 2019 page： 106 - 108 2019.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：2019 Electron Devices Technology and Manufacturing Conference, EDTM 2019

Effect of drift layer thicknesses (DLT) (2, 15 and 30 μm) in reverse current conduction mechanisms of vertical GaN-on-GaN Schottky Barrier Diodes grown MOCVD has been investigated for the first time. The conduction mechanism is changing from thermionic field emission (TFE) to thermionic emission (TE) when the DLT of GaN increases. The SBDs with DLT of 2 μm and 30 μm exhibit TFE through Poole-Frenkel emission and TE, respectively. However, the SBDs with DLT of 15 μm exhibit both TFE and TE. Activation energy (Ea) of traps was also calculated to be 0.69 eV for 2 μm, 0.38 for 15 μm and 0.4 eV for 30 μm respectively. Ea of 0.69 eV and 0.4 eV could be associated with screw threading dislocations and the presence of Mg in the grown drift layer, respectively.

DOI： 10.1109/EDTM.2019.8731215

Observation of Dopant Concentration in GaN Semiconductor by High Sensitivity Electron Holography

Electronic structure analysis at threading dislocation and at m-plane surface of nanopipes in GaN thin films

Nakano Takashi, Chokawa Kenta, Araidai Masaaki, Shiraishi Kenji, Oshiyama Atsushi, Usami Shigeyoshi, Kusaba Akira, Kangawa Yoshihiro, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

JSAP Annual Meetings Extended Abstracts Vol. 2019.1 ( 0 ) page： 3122 - 3122 2019.2

Morphological study of InGaN on GaN substrate by supersaturation Open Access

Liu Zhibin, Nitta Shugo, Robin Yoann, Kushimoto Maki, Deki Manato, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

JOURNAL OF CRYSTAL GROWTH Vol. 508 page： 58-65 2019.2

How to obtain metal-polar untwinned high-quality (10-13) GaN on m-plane sapphire Open Access

Hu Nan, Dinh Duc V., Pristovsek Markus, Honda Yoshio, Amano Hiroshi

JOURNAL OF CRYSTAL GROWTH Vol. 507 page： 205 - 208 2019.2

Nakano Kiyotaka, Matsumoto Miko, Anada Satoshi, Yamamoto Kazuo, Ishikawa Yukari, Hirayama Tsukasa, Ando Yuto, Ogura Masaya, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

Materia Japan Vol. 58 ( 2 ) page： 103 - 103 2019.2

Pole figure analysis from electron backscatter diffraction-an effective method of evaluating fiber-textured silicon thin films as seed layers for epitaxy

Hainey Mel Jr., Robin Yoann, Amano Hiroshi, Usami Noritaka

APPLIED PHYSICS EXPRESS Vol. 12 ( 2 ) 2019.2

Vertical GaN p-n diode with deeply etched mesa and the capability of avalanche breakdown Open Access

Fukushima Hayata, Usami Shigeyoshi, Ogura Masaya, Ando Yuto, Tanaka Atsushi, Deki Manato, Kushimoto Maki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 12 ( 2 ) page： 026502 2019.2

Compositional control of homogeneous InGaN nanowires with the In content up to 90%

Zeghouane Mohammed, Avit Geoffrey, Andre Yamina, Bougerol Catherine, Robin Yoann, Ferret Pierre, Castelluci Dominique, Gil Evelyne, Dubrovskii Vladimir G., Amano Hiroshi, Trassoudaine Agnes

NANOTECHNOLOGY Vol. 30 ( 4 ) page： 044001 2019.1

Localization and transient emission properties in InGaN/ GaN quantum wells of different polarities within core- shell nanorods

Robin Y., Evropeitsev E. A., Shubina T. V., Kirilenko D. A., Davydov V. Yu., Smirnov A. N., Toropov A. A., Eliseyev I. A., Bae S. Y., Kushimoto M., Nitta S., Ivanov S. V., Amano H.

NANOSCALE Vol. 11 ( 1 ) page： 193 - 199 2019.1

Carrier localization structure combined with current micropaths in AlGaN quantum wells grown on an AIN template with macrosteps

Kojima K., Nagasawa Y., Hirano A., Ippommatsu M., Honda Y., Amano H., Akasaki I., Chichibu S. F.

APPLIED PHYSICS LETTERS Vol. 114 ( 1 ) page： 011102 2019.1

286 nm monolithic multicomponent system

Yuan Jialei, Jiang Yan, Shi Zheng, Gao Xumin, Wang Yongjin, Sun Xiaojuan, Li Dabing, Liu Yuhuai, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 58 ( 1 ) page： 010909 2019.1

Electronic structure analysis of core structures of threading dislocations in GaN

Nakano Takashi, Chokawa Kenta, Araidai Masaaki, Shiraishi Kenji, Oshiyama Atsushi, Kusaba Akira, Kangawa Yoshihiro, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

2019 COMPOUND SEMICONDUCTOR WEEK (CSW) page： . 2019

Light-Emitting Diodes Materials, Processes, Devices and Applications Foreword

Amano, H

LIGHT-EMITTING DIODES: MATERIALS, PROCESSES, DEVICES AND APPLICATIONS Vol. 4 page： V - V 2019

MOVPE growth and high-temperature annealing of (10(1)over-bar0) AlN layers on (10(1)over-bar0) sapphire Open Access

Dinh Duc V., Amano Hiroshi, Pristovsek Markus

JOURNAL OF CRYSTAL GROWTH Vol. 502 page： 14-18 2018.11

What is red? On the chromaticity of orange-red InGaN/GaN based LEDs Open Access

Robin Y., Pristovsek M., Amano H., Oehler F., Oliver R. A., Humphreys C. J.

JOURNAL OF APPLIED PHYSICS Vol. 124 ( 18 ) page： 183102 2018.11

Simultaneous Growth of Various InGaN/GaN Core-Shell Microstructures for Color Tunable Device Applications

Robin Yoann, Liao Yaqiang, Pristovsek Markus, Amano Hiroshi

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 215 ( 21 ) page： 1800361 2018.11

Analysis of negative electron affinity InGaN photocathode by temperature-programed desorption method

Kashima Masahiro, Sato Daiki, Koizumi Atsushi, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi, Iijima Hokuto, Meguro Takashi

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Vol. 36 ( 6 ) page： 06JK02 2018.11

Full-duplex light communication with a monolithic multicomponent system Open Access

Wang Yongjin, Wang Xin, Zhu Bingcheng, Shi Zheng, Yuan Jialei, Gao Xumin, Liu Yuhuai, Sun Xiaojuan, Li Dabing, Amano Hiroshi

LIGHT-SCIENCE & APPLICATIONS Vol. 7 page： 83 2018.10

Crystal engineering by tuning the growth kinetics of GaN 3-D microstructures in SAG-HVPE

Avit Geoffrey, Zeghouane Mohammed, Andre Yamina, Castelluci Dominique, Gil Evelyne, Bae Si-Young, Amano Hiroshi, Trassoudaine Agnes

CRYSTENGCOMM Vol. 20 ( 40 ) page： 6207 - 6213 2018.10

Comparing high-purity c- and m-plane GaN layers for Schottky barrier diodes grown homoepitaxially by metalorganic vapor phase epitaxy

Nagamatsu Kentaro, Ando Yuto, Ye Zheng, Barry Ousmane, Tanaka Atsushi, Deki Manato, Nitta Shugo, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 57 ( 10 ) page： 105501 2018.10

High-temperature thermal annealing of nonpolar (10(1)over-bar0) AlN layers sputtered on (1 0(1)over-bar0) sapphire Open Access

Dinh Duc V, Hu Nan, Honda Yoshio, Amano Hiroshi, Pristovsek Markus

JOURNAL OF CRYSTAL GROWTH Vol. 498 page： 377-380 2018.9

Advantages of GaN and Related Materials over Si and Issues to be Solved

AMANO Hiroshi

Vacuum and Surface Science Vol. 61 ( 9 ) page： 565 - 567 2018.9

Detailed study of effects of duration of pre-AIN-growth trimethylaluminum step on morphologies of GaN layers grown on silicon substrate by metal organic chemical vapor deposition

Matsumoto Koji, Ono Toshiaki, Honda Yoshio, Murakami Satoshi, Kushimoto Maki, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 57 ( 9 ) page： 091001 2018.9

Reduction of Residual Impurities in Homoepitaxial m-Plane (10(1)over-bar0) GaN by Using N-2 Carrier Gas in Metalorganic Vapor Phase Epitaxy

Barry Ousmane I, Lekhal Kaddour, Bae Si-Young, Lee Ho-Jun, Pristovsek Markus, Honda Yoshio, Amano Hiroshi

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS Vol. 12 ( 8 ) page： 1800124 2018.8

Improvement of breakdown voltage of vertical GaN p-n junction diode with Ga2O3 passivated by sputtering

Ueoka Yoshihiro, Deki Meneto, Honda Yoshio, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 57 ( 7 ) page： 070302 2018.7

Study on the Main-Chain Structure of Amorphous Fluorine Resins for Encapsulating AlGaN-Based DUV-LEDs

Kiho Yamada, Yosuke Nagasawa, Shoko Nagai, Akira Hirano, Masamichi Ippommatsu, Ko Aosaki, Yoshio Honda, Hiroshi Amano, Isamu Akasaki

Physica Status Solidi (A) Applications and Materials Science Vol. 215 ( 10 ) page： 1700525 2018.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley-VCH Verlag

The main chain structure of optically isotropic amorphous fluorine resin for encapsulating AlGaN-based deep-ultraviolet LEDs (λ &lt
300 nm) is studied. One type of amorphous fluorine resin has a five-membered ring with a single oxygen atom and the other has that one with two oxygen atoms. Reliability testing is performed using AlGaN-based LEDs of 262 and 289 nm. For the resin with two oxygen atoms in the ring, visible damage to the electrode and significantly increased leakage current are considered to been caused by the photolysis of the ring induced by irradiation with deep-ultraviolet light. In contrast, electrode damage and increased leakage are not observed in the case of the resin with the single-oxygen ring.

DOI： 10.1002/pssa.201700525

Interface amorphization in hexagonal boron nitride films on sapphire substrate grown by metalorganic vapor phase epitaxy Open Access

Insight into the performance of multi-color InGaN/GaN nanorod light emitting diodes Open Access

Robin Y., Bae S. Y., Shubina T. V., Pristovsek M., Evropeitsev E. A., Kirilenko D. A., Davydov V. Yu., Smirnov A. N., Toropov A. A., Jmerik V. N., Kushimoto M., Nitta S., Ivanov S. V., Amano H.

SCIENTIFIC REPORTS Vol. 8 page： 7311 2018.5

m-Plane GaN Schottky Barrier Diodes Fabricated With MOVPE Layer on Several Off-Angle m-Plane GaN Substrates Open Access

Atsushi Tanaka, Yuto Ando, Kentaro Nagamatsu, Manato Deki, Heajeong Cheong, Barry Ousmane, Maki Kushimoto, Shugo Nitta, Yoshio Honda, Hiroshi Amano

Physica Status Solidi (A) Applications and Materials Science Vol. 215 ( 9 ) page： 1700645 2018.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley-VCH Verlag

In this study, GaN m-plane Schottky barrier diodes are fabricated by metalorganic vapor-phase epitaxy (MOVPE) on several off-angle gallium nitride (GaN) substrates, and the off-cut angle dependence of impurity incorporation is investigated. We show that the MOVPE layer on the substrate inclined 5° toward the [000–1] direction has extremely low impurity incorporation. These results provide important suggestions for the fabrication of m-plane power devices.

DOI： 10.1002/pssa.201700645

Xu Yang, Shugo Nitta, Markus Pristovsek, Yuhuai Liu, Kentaro Nagamatsu, Maki Kushimoto, Yoshio Honda, Hiroshi Amano

Applied Physics Express Vol. 11 ( 5 ) page： 051002 2018.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Applied Physics

Hexagonal boron nitride (h-BN) films directly grown on c-plane sapphire substrates by pulsed-mode metalorganic vapor phase epitaxy exhibit an interlayer for growth temperatures above 1200 °C. Cross-sectional transmission electron microscopy shows that this interlayer is amorphous, while the crystalline h-BN layer above has a distinct orientational relationship with the sapphire substrate. Electron energy loss spectroscopy shows the energy-loss peaks of B and N in both the amorphous interlayer and the overlying crystalline h-BN layer, while Al and O signals are also seen in the amorphous interlayer. Thus, the interlayer forms during h-BN growth through the decomposition of the sapphire at elevated temperatures.

DOI： 10.7567/APEX.11.051002

Transferrable monolithic multicomponent system for near-ultraviolet optoelectronics Open Access

Chuan Qin, Xumin Gao, Jialei Yuan, Zheng Shi, Yuan Jiang, Yuhuai Liu, Yongjin Wang, Hiroshi Amano

Applied Physics Express Vol. 11 ( 5 ) page： 051201 2018.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Japan Society of Applied Physics

A monolithic near-ultraviolet multicomponent system is implemented on a 0.8-mm-diameter suspended membrane by integrating a transmitter, waveguide, and receiver into a single chip. Two identical InGaN/Al0.10Ga0.90N multiple-quantum well (MQW) diodes are fabricated using the same process flow, which separately function as a transmitter and receiver. There is a spectral overlap between the emission and detection spectra of the MQW diodes. Therefore, the receiver can respond to changes in the emission of the transmitter. The multicomponent system is mechanically transferred from silicon, and the wire-bonded transmitter on glass experimentally demonstrates spatial light transmission at 200 Mbps using non-return-to-zero on–off keying modulation.

DOI： 10.7567/APEX.11.051201

Correlation between dislocations and leakage current of p-n diodes on a free-standing GaN substrate

Shigeyoshi Usami, Yuto Ando, Atsushi Tanaka, Kentaro Nagamatsu, Manato Deki, Maki Kushimoto, Shugo Nitta, Yoshio Honda, Hiroshi Amano, Yoshihiro Sugawara, Yong-Zhao Yao, Yukari Ishikawa

APPLIED PHYSICS LETTERS Vol. 112 ( 18 ) page： 182106 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Dislocations that cause a reverse leakage current in vertical p-n diodes on a GaN free-standing substrate were investigated. Under a high reverse bias, dot-like leakage spots were observed using an emission microscope. Subsequent cathodoluminescence (CL) observations revealed that the leakage spots coincided with part of the CL dark spots, indicating that some types of dislocation cause reverse leakage. When etch pits were formed on the dislocations by KOH etching, three sizes of etch pits were obtained (large, medium, and small). Among these etch pits, only the medium pits coincided with leakage spots. Additionally, transmission electron microscopy observations revealed that pure screw dislocations are present under the leakage spots. The results revealed that lc pure screw dislocations are related to the reverse leakage in vertical p-n diodes. Published by AIP Publishing.

DOI： 10.1063/1.5024704

Chronicity of Anterior Cruciate Ligament Deficiency, Part 1: Effects on the Tibiofemoral Relationship Before and Immediately After Anatomic ACL Reconstruction With Autologous Hamstring Grafts Open Access

Light output performance of red AlGaInP-based light emitting diodes with different chip geometries and structures Open Access

Oh Jeong-Tak, Lee Sang-Youl, Moon Yong-Tae, Moon Ji Hyung, Park Sunwoo, Hong Ki Yong, Song Ki Young, Oh Chan-Hyoung, Shim Jong-In, Jeong Hwan-Hee, Song June-O, Amano Hiroshi, Seong Tae-Yeon

OPTICS EXPRESS Vol. 26 ( 9 ) page： 11194-11200 2018.4

The 2018 GaN power electronics roadmap Open Access

H. Amano, Y. Baines, E. Beam, Matteo Borga, T. Bouchet, Paul R Chalker, M. Charles, Kevin J Chen, Nadim Chowdhury, Rongming Chu, Carlo De Santi, Maria Merlyne De Souza, Stefaan Decoutere, L. Di Cioccio, Bernd Eckardt, Takashi Egawa, P. Fay, Joseph J Freedsman, L. Guido, Oliver Häberlen, Geoff Haynes, Thomas Heckel, Dilini Hemakumara, Peter Houston, Jie Hu, Mengyuan Hua, Qingyun Huang, Alex Huang, Sheng Jiang, H. Kawai, Dan Kinzer, Martin Kuball, Ashwani Kumar, Kean Boon Lee, Xu Li, Denis Marcon, Martin März, R. McCarthy, Gaudenzio Meneghesso, Matteo Meneghini, E. Morvan, A. Nakajima, E. M.S. Narayanan, Stephen Oliver, Tomás Palacios, Daniel Piedra, M. Plissonnier, R. Reddy, Min Sun, Iain Thayne, A. Torres, Nicola Trivellin, V. Unni, Michael J Uren, Marleen Van Hove, David J Wallis, J. Wang, J. Xie, S. Yagi, Shu Yang, C. Youtsey, Ruiyang Yu, Enrico Zanoni, Stefan Zeltner, Yuhao Zhang

Journal of Physics D: Applied Physics Vol. 51 ( 16 ) page： 163001 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Physics Publishing

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

DOI： 10.1088/1361-6463/aaaf9d

Analysis of Cesium Layer on InGaN by Temperature Programmed Desorption Method

Kashima Masahiro, Daiki Sato, Atsushi Koizumi, Tomohiro Nishitani, Yoshio Honda, Hiroshi Amano, Hokuto Iijima, Takashi Meguro

JSAP Annual Meetings Extended Abstracts Vol. 2018.1 ( 0 ) page： 1670 - 1670 2018.3

Tanaka, Y; Kita, K; Takao, R; Amano, H; Uchida, R; Shiozaki, Y; Yonetani, Y; Kinugasa, K; Mae, T; Horibe, S

ORTHOPAEDIC JOURNAL OF SPORTS MEDICINE Vol. 6 ( 1 ) 2018.1

Growth of hexagonal boron nitride on sapphire substrate by pulsed-mode metalorganic vapor phase epitaxy Open Access

Xu Yang, Shugo Nitta, Kentaro Nagamatsu, Si-Young Bae, Ho-Jun Lee, Yuhuai Liu, Markus Pristovsek, Yoshio Honda, Hiroshi Amano

JOURNAL OF CRYSTAL GROWTH Vol. 482 ( 15 ) page： 1 - 8 2018.1

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Hexagonal boron nitride (h-BN) was directly grown on sapphire substrate using alternating ammonia (NH3) and triethylboron (TEB) supply (pulsed mode) in metalorganic vapor phase epitaxy. The best condition is when just enough NH3 is supplied to fully convert the TEB within one cycle. Excess NH3 caused islands on h-BN film surface while a lack of NH3 does not form h-BN at all. The epitaxial relationship between grown h-BN layer and c-plane sapphire was confirmed to be [0001](h-BN)||[0001](sapphire) and [10-10](h-BN)||[11-20](sapphire). It is known that, compared to AlN, BN requires higher V/III ratios for good crystallinity, which due to severe gas-phase reactions is difficult to achieve using continuous supply. Thus using pulsed mode the FWHM of the symmetric (0002) diffraction was almost halved and the growth rate was several times faster. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2017.10.036

Electrical and Thermal Analysis of Vertical GaN-on-GaN PN Diodes

Yates Luke, Pavlidis Georges, Graham Samuel, Usami Shigeyoshi, Nagamatsu Kentaro, Honda Yoshio, Amano Hiroshi

PROCEEDINGS OF THE 17TH IEEE INTERSOCIETY CONFERENCE ON THERMAL AND THERMOMECHANICAL PHENOMENA IN ELECTRONIC SYSTEMS (ITHERM 2018) page： 831 - 837 2018

Theoretical Study of the Electronic Structure of Threading Edge Dislocations in GaN

Nakano Takashi, Araidai Masaaki, Shiraishi Kenji, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

GALLIUM NITRIDE AND SILICON CARBIDE POWER TECHNOLOGIES 8 Vol. 86 ( 12 ) page： 41 - 49 2018

DFT modeling of carbon incorporation in GaN(0001) and GaN(000(1)over-bar) metalorganic vapor phase epitaxy Reviewed

Pawel Kempisty, Yoshihiro Kangawa, Akira Kusaba, Kenji Shiraishi, Stanislaw Krukowski, Michal Bockowski, Koichi Kakimoto, and Hiroshi Amano

APPLIED PHYSICS LETTERS Vol. 111 page： 141602/1-5 2017.10

Language：English Publishing type：Research paper (scientific journal)

The carbon incorporation mechanism in GaN(0001) and GaN(000 (1) over bar) during MOVPE was investigated using density functional theory (DFT) calculations. The results confirm that the crucial factors for carbon incorporation are Fermi level pinning and accompanying surface band bending. In addition, the lattice symmetry has a strong dependence on the stability of carbon in a few subsurface layers, which results from interactions between the impurities and surface states. It was shown that these effects are responsible for facilitating or hindering the incorporation of impurities and dopants. The influence of diluent gas species (hydrogen or nitrogen) on carbon incorporation was discussed.

DOI： 10.1063/1.4991608

Initial leakage current paths in the vertical-type GaN-on-GaN Schottky barrier diodes

Liwen Sang, Bing Ren, Masatomo Sumiya, Meiyong Liao, Yasuo Koide, Atsushi Tanaka, Yujin Cho, Yoshitomo Harada, Toshihide Nabatame, Takashi Sekiguchi, Shigeyoshi Usami, Yoshio Honda, and Hiroshi Amano

APPLIED PHYSICS LETTERS Vol. 111 page： 122102/1-5 2017.9

Language：English Publishing type：Research paper (scientific journal)

Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations with a screw-type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current-voltage characteristics.

DOI： 10.1063/1.4994627

Absolute technique for measuring internal electric fields in InGaN/GaN light-emitting diodes by electroreflectance applicable to all crystal orientations Reviewed

Tomoyuki Tanikawa, Kanako Shojiki, Ryuji Katayama, Shigeyuki Kuboya, Takashi Matsuoka, Yoshio Honda, and Hiroshi Amano

Applied Physics Express Vol. 10 page： 082101/1-4 2017.8

Low cost high voltage GaN polarization superjunction field effect transistors Open Access

H. Kawai, S. Yagi, S. Hirata, F. Nakamura, T. Saito, Y. Kamiyama, M. Yamamoto, H. Amano, V. Unni, E. M. S. Narayanan

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 214 ( 8 ) page： 1600834/1-10 2017.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

A comprehensive overview of the novel high voltage GaN field effect transistors (FETs) based on the Polarization Superjunction (PSJ) concept, and a cost-effective approach towards manufacturing these high performance devices are presented. Current challenges impeding wider adoption of GaN power switching transistors in applications, and the latest results of the scaled-up PSJ-FETs from POWDEC KK, are also discussed. The article also presents hard-switching characteristics of 400-800V boost converter, constructed using a PSJ-FET grown on sapphire substrate, and the future direction of GaN power semiconductor technology based on monolithic integration for advanced power electronics.

DOI： 10.1002/pssa.201600834

Effect of dislocations on the growth of p-type GaN and on the characteristics of p-n diodes

Facet dependence of leakage current and carrier concentration in m-plane GaN Schottky barrier diode fabricated with MOVPE Reviewed

Atsushi Tanaka, Ousmane1 Barry, Kentaro Nagamatsu, Junya Matsushita, Manato Deki, Yuto Ando, Maki Kushimoto, Shugo Nitta, Yoshio Honda, and Hiroshi Amano

Phys. Status Solidi A Vol. 214 ( 8 ) page： 1600829/1-5 2017.8

Language：English Publishing type：Research paper (scientific journal)

In this study, GaN m-plane Schottky barrier diodes fabricated with a metalorganic vapor-phase epitaxy on a GaN substrate were investigated using emission microscope, photoluminescence, and cathodoluminescence. In addition, facet dependence of leakage current under reverse-biased condition was observed. We showed that the leakage-current distribution was caused by the facet dependence of the carrier concentration and oxygen concentration. These results can provide important suggestions for the fabrication of m-plane devices. (a) four-faceted hillocks on m-plane GaN MOVPE sample, facet dependence of (b) leakage current and (c) PL peak intensity of the m-plane GaN Schottky barrier diode.

DOI： 10.1002/pssa.201600829

Effect of dislocations on the growth of p-type GaN and on the characteristics of p-n diodes Invited Reviewed

Shigeyoshi Usami, Ryosuke Miyagoshi, Atsushi Tanaka, Kentaro Nagamatsu, Maki Kushimoto, Manato Deki, Shugo Nitta, Yoshio Honda, and Hiroshi Amano

Phys. Status Solidi A Vol. 214 ( 8 ) page： 1600837/1-5 2017.8

Language：English Publishing type：Research paper (scientific journal)

We investigate the influence of crystal defects on p-type GaN grown by metalorganic vapor phase epitaxy. Sets of p-type GaN films were grown on sapphire substrates and on free-standing GaN (F-GaN) substrates simultaneously using various Et-Cp2Mg flow rates. Although there is a difference of two orders of magnitude between the threading dislocation densities of p-type GaN grown on sapphire and F-GaN substrates, there is no significant difference in hole concentration. However, there are problems with the surface morphology of p-type GaN grown on sapphire. The deterioration of the surface was caused by the difference in nanopipe density. The electrical properties of a p-n junction diode formed on sapphire with a high density of nanopipes were observed using emission microscopy under both forward- and reverse-bias conditions. Our results demonstrate that the nanopipes are electrically inactive, and that other types of threading dislocation have more influence on the current-voltage characteristics.

DOI： 10.1002/pssb.201600722

Selective-area growth of doped GaN nanorods by pulsed-mode MOCVD: Effect of Si and Mg dopants Reviewed

Si-Young Bae, Kaddour Lekhal, Ho-Jun Lee, Jung-Wook Min, Dong-Seon Lee, Yoshio Honda, and Hiroshi Amano

Phys. Status Solidi B Vol. 254 ( 8 ) page： 1600722/1-7 2017.8

Language：English Publishing type：Research paper (scientific journal)

Injecting current with a uniform carrier concentration is important for applications with three-dimensional architectures such as vertical power devices or displays. In III-nitride nanostructures, dopants not only incorporate differently depending on the surface orientation but can also seriously affect the kinetic equilibrium shapes of the nanorods. Herein, we report selective-area growth of doped GaN nanorods grown by pulsed-mode metalorganic chemical vapor deposition. Two dopants, Si and Mg, were employed as donor and acceptor atoms, respectively, for a mono-doping approach. Furthermore, a mixed flow of Si and Mg was supplied for a co-doping approach. We compared the morphological effects and growth rates of each doped GaN nanorod array. Then, we proposed appropriate growth mechanisms for the doped GaN nanorods on the basis of our structural characterizations. These results might extend the morphological functionality of GaN nanorods by including doping and may also provide an appropriate foundation for the design of nanostructure-based electronic or photonic devices.

DOI： 10.1002/pssb.201600722

Decomposition of trimethylgallium and adduct formation in a metalorganic vapor phase epitaxy reactor analyzed by high-resolution gas monitoring system Reviewed

Kentaro Nagamatsu, Shugo Nitta, Zheng Ye, Hirofumi Nagao, Shinichi Miki, Yoshio Honda, and Hiroshi Amano

Phys. Status Solidi B Vol. 254 ( 8 ) page： 1600737/1-4 2017.8

Usami Shigeyoshi, Miyagoshi Ryosuke, Tanaka Atsushi, Nagamatsu Kentaro, Kushimoto Maki, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 214 ( 8 ) 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

We investigate the influence of crystal defects on p-type GaN grown by metalorganic vapor phase epitaxy. Sets of p-type GaN films were grown on sapphire substrates and on free-standing GaN (F-GaN) substrates simultaneously using various Et-Cp2Mg flow rates. Although there is a difference of two orders of magnitude between the threading dislocation densities of p-type GaN grown on sapphire and F-GaN substrates, there is no significant difference in hole concentration. However, there are problems with the surface morphology of p-type GaN grown on sapphire. The deterioration of the surface was caused by the difference in nanopipe density. The electrical properties of a p–n junction diode formed on sapphire with a high density of nanopipes were observed using emission microscopy under both forward- and reverse-bias conditions. Our results demonstrate that the nanopipes are electrically inactive, and that other types of threading dislocation have more influence on the current–voltage characteristics.

DOI： 10.1002/pssa.201600837

Selective-area growth of vertically oriented GaN nanostructures with a hafnium pre-orienting layer Reviewed

Role of threading dislocations in strain relaxation during GaInN growth monitored by real-time X-ray reflectivity Reviewed

Guangxu Ju, Masao Tabuchi, Yoshikazu Takeda, and Hiroshi Amano

Applied Physics Letters Vol. 110 ( 26 ) page： 262105/1-5 2017.6

A-plane GaN growth on (11-20) 4H-SiC substrate with an ultrathin interlayer Reviewed

Zheng Sun, Peifeng Song, Shugo Nitta, Yoshio Honda, Hiroshi Amano

Journal of Crystal Growth Vol. 468 page： 866-869 2017.6

S.-Y.Bae, K. Lekhal, H.-J.Lee, T.Mitsunari, J.-W.Min, D.-S.Leed, M.Kushimoto, Y.Honda, H.Amano

Journal of Crystal Growth Vol. 468 page： 110-113 2017.6

Orientation-controlled epitaxial lateral overgrowth of semipolar GaN on Si(001) with a directionally sputtered AlN buffer layer Reviewed

Ho-Jun Lee, Si-Young Bae, Kaddour Lekhal, Akira Tamura, Takafumi Suzuki, Maki Kushimoto, Yoshio Honda, and Hiroshi Amano

Journal of Crystal Growth Vol. 468 page： 547-551 2017.6

Effect of V/III ratio on the surface morphology and electrical properties of m–plane ( 101¯0 ) GaN homoepitaxial layers Reviewed

Vol. 468 page： 552-556 2017.6

Language：English Publishing type：Research paper (scientific journal)

We have investigated the effect of V/III ratio on the surface morphology, impurity concentration and electrical properties of m–plane (101¯0) Gallium Nitride (GaN) homoepitaxial layers. Four-sided pyramidal hillocks are observed on the nominally on-axis m–plane GaN films. Hillocks sizes relatively increase by increasing the V/III ratio. All facets of pyramidal hillocks exhibit well-defined step-terrace features. Secondary ion mass spectrometry depth profiles reveal that carbon impurities decrease by increasing the V/III ratio while the lowest oxygen content is found at an optimized V/III ratio of 900. Vertical Schottky barrier diodes fabricated on the m–GaN samples were characterized. Low leakage current densities of the order of 10−10 A/cm2 at −5 V are obtained at the optimum V/III ratio. Oxygen impurities and screw-component dislocations around hillocks are found to have more detrimental impact on the leakage current mechanism.

DOI： 10.1016/j.jcrysgro.2016.12.012

Annealing eﬀect on threading dislocations in a GaN grown on Si substrate Reviewed

Vol. 468 page： 835-838 2017.6

Language：English Publishing type：Research paper (scientific journal)

Eﬀect of rapid thermal annealing (RTA) on crystal defects in a GaN layer grown on a (111)Si substrate was investigated by photoluminescence (PL) and transmission electron microscopy (TEM) analyses. The PL spectra suggested that the density of gallium vacancy is not changed by the heat treatment up to 700 °C. In the TEM specimen, we had dislocation half loops generated by oﬀ-axis propagation of the threading dislocation. We found that the half-loop of c-type dislocation shrinks/moves by a repetitive RTA at 600–700 °C. In contrast, we could ﬁnd no remarkable changes in the a-type or a+c-type dislocations.

DOI： 10.1016/j.jcrysgro.2017.01.001

A-plane GaN growth on (11-20) 4H-SiC substrate with an ultrathin interlayer

Sun Zheng, Song Peifeng, Nitta Shugo, Honda Yoshio, Amano Hiroshi

JOURNAL OF CRYSTAL GROWTH Vol. 468 page： 866 - 869 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth

A-plane GaN was attempted to be grown on (11-20) 4H-SiC bulk substrate without using a traditional thick buffer layer. By inducing TMAl treatment before the GaN growth step and using both a low pressure and V/III ratio, the interlayer thickness of the a-plane GaN/SiC was reduced to 1.7+0.5 nm. The ultrathin interlayer was observed to be either AlN or AlGaN with a low Ga composition. This study is aimed to contribute to the understanding of GaN growth on the sidewalls of c-plane trench structure SiC. The ultrathin growth technique is also hoped to be applied to the fabrication of GaN-based vertical structure nonpolar optical or electrical devices.

DOI： 10.1016/j.jcrysgro.2017.01.031

Uneven AlGaN multiple quantum well for deep-ultraviolet LEDs grown on macrosteps and impact on electroluminescence spectral output Reviewed

Michiko Kaneda, Cyril Pernot, Yosuke Nagasawa, Akira Hirano, Masamichi Ippommatsu, Yoshio Honda, Hiroshi Amano, and Isamu Akasaki

Japanese Journal of Applied Physics Vol. 56 page： 061002 2017.5

III-nitride core-shell nanorod array on quartz substrates Open Access

Si-Young Bae, Jung-Wook Min, Hyeong-Yong Hwang, Kaddour Lekhal, Ho-Jun Lee, Young-Dahl Jho, Dong-Seon Lee, Yong-Tak Lee, Nobuyuki Ikarashi, Yoshio Honda, Hiroshi Amano

SCIENTIFIC REPORTS Vol. 7 page： 45345 2017.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

We report the fabrication of near-vertically elongated GaN nanorods on quartz substrates. To control the preferred orientation and length of individual GaN nanorods, we combined molecular beam epitaxy (MBE) with pulsed-mode metal-organic chemical vapor deposition (MOCVD). The MBE-grown buffer layer was composed of GaN nanograins exhibiting an ordered surface and preferred orientation along the surface normal direction. Position-controlled growth of the GaN nanorods was achieved by selective-area growth using MOCVD. Simultaneously, the GaN nanorods were elongated by the pulsed-mode growth. The microstructural and optical properties of both GaN nanorods and InGaN/GaN core-shell nanorods were then investigated. The nanorods were highly crystalline and the core-shell structures exhibited optical emission properties, indicating the feasibility of fabricating III-nitride nano-optoelectronic devices on amorphous substrates.

DOI： 10.1038/srep45345

Investigation of reduction of light absorption at p-side toward UV emitting devices

Yasuda Toshiki, Kuwabara Natsuko, Takeuchi Tetsuya, Iwaya Motoaki, Kamiyama Satoshi, Akasaki Isamu, Amano Hiroshi

JSAP Annual Meetings Extended Abstracts Vol. 2017.1 ( 0 ) page： 3400 - 3400 2017.3

Effect of thermal treatment on the quantu efficiency of NEA-InGaN photocatode

Kashima Masahiro, Iijima Hokuto, Nishitani Tomohiro, Sato Daiki, Honda Yoshio, Amano Hiroshi, Meguro Takashi

JSAP Annual Meetings Extended Abstracts Vol. 2017.1 ( 0 ) page： 1554 - 1554 2017.3

A Study on the Photo-resistance and the Decomposition Mechanism of Perfluoro Resins Applied to Encapsulating Deep Ultra Violet LEDs

Nagasawa Yosuke, Yamada Kiho, Nagai Shouko, Hirano Akira, Ipponmatsu Masamichi, Aosaki Ko, Honda Yoshio, Amano Hiroshi, Akasaki Isamu

JSAP Annual Meetings Extended Abstracts Vol. 2017.1 ( 0 ) page： 1136 - 1136 2017.3

Relationship between lattice relaxation and electrical properties in polarization doping of graded AlGaN with high AlN mole fraction on AlGaN template

Yasuda Toshiki, Takeuchi Tetsuya, Iwaya Motoaki, Kamiyama Satoshi, Akasaki Isamu, Amano Hiroshi

APPLIED PHYSICS EXPRESS Vol. 10 ( 2 ) 2017.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

We investigated polarization doping for hole generation in abrupt and graded GaN/Al0.7Ga0.3N interfaces on Al0.99Ga0.01N templates. The abrupt interface exhibited hole generation, whereas the graded interface exhibited electron generation. In the graded AlxGa1%xN (x = 0.65-0), a graded part with an AlN mole fraction ranging from 0.2 to 0 showed a large relaxation. Theoretical estimation revealed that this part contained positive polarization charges, accumulating electrons. Via Mg doping in the graded AlGaN layer, we obtained a high hole concentration of 3 ' 1013cm%2. These results indicate that understanding the relaxation conditions in the graded layer is indispensable for polarization doping.

DOI： 10.7567/APEX.10.025502

Relationship between lattice relaxation and electrical properties in polarization doping of graded AlGaN with high AlN mole fraction on AlGaN template Reviewed

Toshiki Yasuda, Tetsuya Takeuchi, Motoaki Iwaya, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

Applied Physics Express Vol. 10 page： 025502 2017.1

From the dawn of gan-based light-emitting devices to the present day

Amano H.

Handbook of Solid-State Lighting and LEDs page： 3-12 2017.1

High quality Al0.99Ga0.01N layers on sapphire substrates grown at 1150 degrees C by metalorganic vapor phase epitaxy

Katsuno Shota, Yasuda Toshiki, Hagiwara Koudai, Koide Norikatsu, Iwaya Motoaki, Takeuchi Tetsuya, Kamiyama Satoshi, Akasaki Isamu, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 56 ( 1 ) 2017.1

Reduction of Dislocations in GaN on Silicon Substrate Using In Situ Etching Reviewed Open Access

Koji Matsumoto, Toshiaki Ono, Yoshio Honda, Tetsuya Yamamoto, Shigeyoshi Usami, Maki Kushimoto, Satoshi Murakami, and Hiroshi Amano

Physica Status Solidi b Vol. 253 page： 1700387(1-7) 2017

Language：English Publishing type：Research paper (scientific journal)

A gallium nitride (GaN) epitaxial layer with a low density of threading dislocations is successfully grown on a silicon substrate by using in situ gas
etching. Silicon nitride (SiNx) film is used as a mask, and ammonia is intermittently supplied in hydrogen ambient during the etching. After etching,
high-density deep pits appeared on the surface of a GaN template layer and corresponded to the threading dislocations in the layer. In this novel method,
before growing an additional GaN layer on the template GaN layer, a second SiNx layer is deposited after the etching process, and this layer prevents GaN nuclei from growing on the upper side-walls of the pits. By using this method, the density of threading dislocations of the GaN surface is reduced to 6.7E7 cm2. This method is cost effective, completing all the necessary processes in one growth run without taking samples out from a metalorganic chemical vapor deposition (MOCVD) reactor.

DOI： 10.1002/pssb.201700387

Development of Sustainable Smart Society based on Transformative Electronics

Ogura M., Ando Y., Usami S., Nagamatsu K., Kushimoto M., Deki M., Tanaka A., Nitta S., Honda Y., Pristovsek M., Kawai H., Yagi S., Amano H.

2017 IEEE INTERNATIONAL ELECTRON DEVICES MEETING (IEDM) page： . 2017

Progress and prospect of growth of wide-band-gap group III nitrides

Hiroshi Amano

Topics in Applied Physics Vol. 133 page： 1 - 9 2017

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Springer Verlag

GaAs, InP, and their related compound semiconductors can be grown on native substrates, whereas such growth was not possible for group III nitride semiconductors in the 1970s and 1980s. Despite this drawback, researchers were able to use novel functions of group III nitride semiconductors by growing their thin films on nonnative substrates such as sapphire SiC and Si.

DOI： 10.1007/978-981-10-3755-9_1

From the Dawn of GaN-Based Light-Emitting Devices to the Present Day

Amano Hiroshi

HANDBOOK OF SOLID-STATE LIGHTING AND LEDS page： 3 - 11 2017

High quality Al0.99Ga0.01N layers on sapphire substrates grown at 1150 °C by metalorganic vapor phase epitaxy Reviewed

Shota Katsuno, Toshiki Yasuda, Koudai Hagiwara, Norikatsu Koide, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, and Hiroshi Amano

Japanese Journal of Applied Physics Vol. 56 page： 015504 2016.12

Improved crystal quality of semipolar (10(1)over-bar3) GaN on Si(001) substrates using AlN/GaN superlattice interlayer Reviewed

Ho-Jun Lee, Si-Young Bae, Kaddour Lekhal, Tadashi Mitsunaria, Akira Tamura, Yoshio Honda, Hiroshi Amano

Journal of Crystal Growth Vol. 454 page： 114-120 2016.11

Controlled morphology of regular GaN microrod arrays by selective area growth with HVPE Reviewed

Kaddour Lekhal, Si-Young Bae, Ho-Jun Lee, Tadashi Mitsunari, Akira Tamura, Manato Deki, Yoshio Honda, Hiroshi Amano

Journal of Crystal Growth Vol. 447 page： 55-61 2016.8

Language：English Publishing type：Research paper (scientific journal)

The selective area growth (SAG) of GaN was implemented on patterned GaN/sapphire templates by hydride vapor phase epitaxy (HVPE) to fabricate regular arrays of Ga-polar GaN microrods. The control of growth parameters such as H2/N2 carrier gas ratio, growth temperature, and absolute NH3/HCl gas flow resulted in changes in the growth morphology.

DOI： 10.1016/j.jcrysgro.2016.05.008

Development of highly durable deep-ultraviolet AlGaN-based LED multichip array with hemispherical encapsulated structures using a selected resin through a detailed feasibility study Reviewed

Shoko Nagai, Kiho Yamada, Akira Hirano, Masamichi Ippommatsu, Masahiro Ito, Naoki Morishima, Ko Aosaki, Yoshio Honda, Hiroshi Amano, and Isamu Akasaki

Japanese Journal of Applied Physics Vol. 55 page： 082101/1-7 2016.8

Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy Reviewed

Tran Thien Duc, Galia Pozina, Hiroshi Amano, Bo Monemar, Erik Janz´en, and Carl Hemmingsson

PHYSICAL REVIEW Vol. B94 page： 045206/1-8 2016.7

Low-ohmic-contact-resistance V-based electrode for n-type AlGaN with high AlN molar fraction Reviewed

Kazuki Mori, Kunihiro Takeda, Toshiki Kusafuka, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

Low-ohmic-contact-resistance V-based electrode for n-type AlGaN with high AlN molar fraction Vol. 55 ( 5S ) page： 05FL03/1-5 2016.5

Observation of relaxation time of surface charge limit for InGaN photocathodes with negative electron affinity Reviewed

Daiki Sato, Tomohiro Nishitani, Yoshio Honda and Hiroshi Amano

Japanese Journal of Applied Physics Vol. 55 ( 5S ) page： 05FH05/1-4 2016.5

Study of radiation detection properties of GaN pn diode Reviewed

Mutsuhito Sugiura, Maki Kushimoto, Tadashi Mitsunari, Kohei Yamashita, Yoshio Honda, Hiroshi Amano, Yoku Inoue, Hidenori Mimura, Toru Aoki, and Takayuki Nakano

Japanese Journal of Applied Physics Vol. 55 page： 05FJ02/1-3 2016.5

Language：English Publishing type：Research paper (scientific journal)

Recently, GaN, which has remarkable properties as a material for optical devices and high power electron devices, has also attracted attention as a material for radiation detectors. We previously suggested the use of BGaN as a neutron detector material. However, the radiation detection characteristics of GaN itself are not yet adequately understood. For realizing a BGaN neutron detector, the understanding of the radiation detection characteristics of GaN, which is a base material of the neutron detector, is important. In this study, we evaluated the radiation detection characteristics of GaN. We performed I V and energy spectrum measurements under alpha ray, gamma ray, and thermal neutron irradiations to characterize the radiation detection characteristics of a GaN diode. The obtained results indicate that GaN is an effective material for our proposed new BGaN-based neutron detector.

DOI： 10.7567/JJAP.55.05FJ02

Emission Characteristics of InGaN/GaN Core-Shell Nanorods Embedded in a 3D Light-Emitting Diode Reviewed Open Access

Byung Oh Jung, Si-Young Bae, Seunga Lee, Sang Yun Kim, Jeong Yong Lee, Yoshio Honda and Hiroshi Amano

Nanoscale Research Letters Vol. 11 2016.4

Language：English Publishing type：Research paper (scientific journal)

We report the selective-area growth of a gallium nitride (GaN)-nanorod-based InGaN/GaN multiple-quantum-well (MQW) core-shell structure embedded in a three-dimensional (3D) light-emitting diode (LED) grown by metalorganic chemical vapor deposition (MOCVD) and its optical analysis. High-resolution transmission electron microscopy (HR-TEM) observation revealed the high quality of the GaN nanorods and the position dependence of the structural properties of the InGaN/GaN MQWs on multiple facets. The excitation and temperature dependences of photoluminescence (PL) revealed the m-plane emission behaviors of the InGaN/GaN core-shell nanorods. The electroluminescence (EL) of the InGaN/GaN core-shell-nanorod-embedded 3D LED changed color from green to blue with increasing injection current. This phenomenon was mainly due to the energy gradient and deep localization of the indium in the selectively grown InGaN/GaN core-shell MQWs on the 3D architecture.

DOI： 10.1186/s11671-016-1441-6