Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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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

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Scopus

Quasi-ballistic thermal conduction in 6H-SiC Reviewed

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

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

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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High-Gain Gated Lateral Power Bipolar Junction Transistor Reviewed

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

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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

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

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

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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

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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

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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

天野浩

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

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

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

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Isamu Akasaki: The Pioneer of Blue LEDs and his Collaboration with <i>pss</i> OBITUARY

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

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

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

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

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PubMed

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

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

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

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Papers - AMANO, Hiroshi