Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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Recent advances in micro-pixel light emitting diode technology Reviewed

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

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 Al<sub>1/2</sub>Ga<sub>1/2</sub>N predicted by Monte-Carlo method based on first-principles calculations Reviewed

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

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

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 <i>n</i>-type gallium nitride layer grown via halogen-free vapor-phase epitaxy Reviewed

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

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

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

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

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

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

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

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