Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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Ohmic Contact to <i>p</i>-Type GaN Enabled by Post-Growth Diffusion of Magnesium

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

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

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

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

<p>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.</p>

DOI： 10.1299/jsmemecj.2022.s055-10

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

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

<p>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.</p>

DOI： 10.1299/jsmemecj.2022.s055-11

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

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

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

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

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

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

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

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

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

Multiple electron beam generation from InGaN photocathode

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

Vertical GaN p<SUP>+</SUP>-n junction diode with ideal avalanche capability grown by halide vapor phase epitaxy (vol 119, 152102, 2021)

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

Amano, H

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

Vertical GaN p<SUP>+</SUP>-n junction diode with ideal avalanche capability grown by halide vapor phase epitaxy

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

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

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

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

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

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

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

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