Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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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.

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

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

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 <i>n-</i>Al<sub>0.6</sub>Ga<sub>0.4</sub>N 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 H<sub>2</sub>O 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<i> <sub>x</sub> </i>Ga<sub>1-<i>x</i> </sub>N (<i>x</i>=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

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