研究者詳細 - 天野　浩

論文 - 天野　浩

分割表示 874 件中 161 - 180 件目／全件表示 >>

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

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

SCIENTIFIC REPORTS 11 巻 ( 1 ) 頁： 6754 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

GaN nanorods (NRds) with axial InGaN/GaN MQWs insertions are synthesized by an original cost-effective and large-scale nanoimprint-lithography process from an InGaN/GaN MQWs layer grown on c-sapphire substrates. By design, such NRds exhibit a single emission due to the c-axis MQWs. A systematic study of the emission of the NRds by time-resolved luminescence (TR-PL) and power dependence PL shows a diameter-controlled luminescence without significant degradation of the recombination rate thanks to the diameter-controlled strain tuning and QSCE. A blueshift up to 0.26 eV from 2.28 to 2.54 eV (543 nm to 488 nm) is observed for 3.2 nm thick InGaN/GaN QWs with an In composition of 19% when the NRds radius is reduced from 650 to 80 nm. The results are consistent with a 1-D based strain relaxation model. By combining state of the art knowledge of c-axis growth and the strong strain relieving capability of NRds, this process enables multiple and independent single-color emission from a single uniform InGaN/GaN MQWs layer in a single patterning step, then solving color mixing issue in InGaN based nanorods LED devices.

DOI： 10.1038/s41598-021-86139-9

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

Kangawa, Y; Kusaba, A; Kempisty, P; Shiraishi, K; Nitta, S; Amano, H

CRYSTAL GROWTH & DESIGN 21 巻 ( 3 ) 頁： 1878 - 1890 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Crystal Growth and Design

To improve the properties of semiconductors, it is necessary to construct an integrated crystal growth model that covers all elementary processes of metal-organic vapor phase epitaxy (MOVPE). Although there are several theoretical models that can reproduce any elemental growth process, they are inadequate for controlling semiconductor epitaxy: the elementary processes of (1) the vapor phase reaction, (2) the surface reaction, and (3) incorporation are entangled with each other. That is, sequential analyses of elementary growth processes from upstream (1) to downstream (3) are indispensable for an understanding of the entire process of MOVPE. In this Review, the recent progress of theoretical models based on calculations from first-principles calculations are summarized. The possibility of predicting carbon concentrations in GaN grown by MOVPE are explored as an example. The results of calculations using a model that integrates (1) → (2) → (3) reproduce the experimental tendencies of carbon incorporation. Calculations show that the contribution of each elementary growth process to a change in carbon concentration can be discussed separately, but the relationship between the input parameters and the resulting outputs can only be determined through experiment. Although this examination explores a special case, the development of a precise integrated crystal growth model would greatly contribute to innovation in semiconductor manufacturing.

DOI： 10.1021/acs.cgd.0c01564

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

Yamada, T; Ando, Y; Watanabe, H; Furusawa, Y; Tanaka, A; Deki, M; Nitta, S; Honda, Y; Suda, J; Amano, H

APPLIED PHYSICS EXPRESS 14 巻 ( 3 ) 頁： 036505 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

Photo-electrochemical (PEC) etching is a promising technique for fabricating GaN microelectromechanical systems devices. In this study, we demonstrate the fabrication of GaN cantilevers by the bandgap-selective PEC etching of an InGaN superlattice sacrificial layer. By using an InGaN superlattice as a sacrifice layer, we found the PEC etching rate became higher than using a normal InGaN layer. As a result, the InGaN superlattice was completely etched and we fabricated GaN-based cantilevers whose resonance characteristics were measured. The Young’s modulus of GaN was determined from the resonance characteristics of GaN cantilevers to be the same as the highest value reported previously.

DOI： 10.35848/1882-0786/abe657

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

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

CRYSTALS 11 巻 ( 3 ) 頁： 1 - 27 2021年3月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Crystals

Thermal boundary conditions for numerical simulations of ammonothermal GaN crystal growth are investigated. A global heat transfer model that includes the furnace and its surroundings is presented, in which fluid flow and thermal field are treated as conjugate in order to fully account for convective heat transfer. The effects of laminar and turbulent flow are analyzed, as well as those of typically simultaneously present solids inside the autoclave (nutrient, baffle, and multiple seeds). This model uses heater powers as a boundary condition. Machine learning is applied to efficiently determine the power boundary conditions needed to obtain set temperatures at specified locations. Typical thermal losses are analyzed regarding their effects on the temperature distribution inside the autoclave and within the autoclave walls. This is of relevance because autoclave wall temperatures are a convenient choice for setting boundary conditions for simulations of reduced domain size. Based on the determined outer wall temperature distribution, a simplified model containing only the autoclave is also presented. The results are compared to those observed using heater-long fixed temperatures as boundary condition. Significant deviations are found especially in the upper zone of the autoclave due to the important role of heat losses through the autoclave head.

DOI： 10.3390/cryst11030254

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

Yasuda, H; Nishitani, T; Ichikawa, S; Hatanaka, S; Honda, Y; Amano, H

QUANTUM BEAM SCIENCE 5 巻 ( 1 ) 頁： 5 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Quantum Beam Science

The development of pulsed electron sources is applied to electron microscopes or electron beam lithography and is effective in expanding the functions of such devices. The laser photocathode can generate short pulsed electrons with high emittance, and the emittance can be increased by changing the cathode substrate from a metal to compound semiconductor. Among the substrates, nitride-based semiconductors with a negative electron affinity (NEA) have good advantages in terms of vacuum environment and cathode lifetime. In the present study, we report the development of a photocathode electron gun that utilizes photoelectron emission from a NEA-InGaN substrate by pulsed laser excitation, and the purpose is to apply it to material nanofabrication and high-speed observation using a pulsed transmission electron microscope (TEM) equipped with it.

DOI： 10.3390/qubs5010005

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

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

APPLIED PHYSICS LETTERS 118 巻 ( 7 ) 頁： 072103 2021年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

The leakage current caused by the Si pileup at the regrowth interface of AlGaN/GaN high electron mobility transistors (HEMTs) is significantly suppressed by the semi-insulating Mg-doped GaN layer. Mg is unintentionally doped and can be originated from the graphite susceptor of metal organic vapor phase epitaxy. Before regrowth of the AlGaN/GaN heterostructure, the GaN template is treated with hydrochloric acid (HCl) and hydrogen peroxide/potassium hydroxide (H2O2/KOH) solution to promote the adsorption of Mg on the GaN surface. The Mg-doped GaN channel layer is highly resistive due to the passivation of hydrogen. The p-n junction formed by the weakly p-type Mg-doped GaN layer and the n-type Si pileup layer depletes the excess electrons at the regrowth interface. As a result, the off-state drain leakage current of the HEMT device can be decreased by two orders of magnitude at 40 V.

DOI： 10.1063/5.0034584

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

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

OPTICAL MATERIALS EXPRESS 11 巻 ( 2 ) 頁： 524 - 524 2021年2月

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

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

IEEE Journal of the Electron Devices Society 9 巻頁： 570 - 581 2021年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Journal of the Electron Devices Society

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

DOI： 10.1109/JEDS.2021.3081463

Development of UV-C laser diodes on AlN substrate

Kushimoto M.

Proceedings of SPIE - The International Society for Optical Engineering 11686 巻 2021年

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

Piva F.

Proceedings of SPIE - The International Society for Optical Engineering 11686 巻 2021年

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

Wang, J; Amano, H; Xie, YH

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

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：2021 5th IEEE Electron Devices Technology and Manufacturing Conference, EDTM 2021

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

DOI： 10.1109/EDTM50988.2021.9420859

Electrical properties of GaN metal-insulator-semiconductor field-effect transistors with Al<sub>2</sub>O<sub>3</sub>/GaN interfaces formed on vicinal Ga-polar and nonpolar surfaces

Ando, Y; Nagamatsu, K; Deki, M; Taoka, N; Tanaka, A; Nitta, S; Honda, Y; Nakamura, T; Amano, H

APPLIED PHYSICS LETTERS 117 巻 ( 24 ) 頁： 242104 2020年12月

The 2020 UV emitter roadmap Open Access

Amano H., Collazo R., De Santi C., Einfeldt S., Funato M., Glaab J., Hagedorn S., Hirano A., Hirayama H., Ishii R., Kashima Y., Kawakami Y., Kirste R., Kneissl M., Martin R., Mehnke F., Meneghini M., Ougazzaden A., Parbrook P.J., Rajan S., Reddy P., Römer F., Ruschel J., Sarkar B., Scholz F., Schowalter L.J., Shields P., Sitar Z., Sulmoni L., Wang T., Wernicke T., Weyers M., Witzigmann B., Wu Y.R., Wunderer T., Zhang Y.

Journal of Physics D: Applied Physics 53 巻 ( 50 ) 頁： 503001 2020年12月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physics D: Applied Physics

Solid state UV emitters have many advantages over conventional UV sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down to 210 nm - due to its large and tuneable direct band gap, n- and p-doping capability up to the largest bandgap material AlN and a growth and fabrication technology compatible with the current visible InGaN-based LED production. However AlGaN based UV-emitters still suffer from numerous challenges compared to their visible counterparts that become most obvious by consideration of their light output power, operation voltage and long term stability. Most of these challenges are related to the large bandgap of the materials. However, the development since the first realization of UV electroluminescence in the 1970s shows that an improvement in understanding and technology allows the performance of UV emitters to be pushed far beyond the current state. One example is the very recent realization of edge emitting laser diodes emitting in the UVC at 271.8 nm and in the UVB spectral range at 298 nm. This roadmap summarizes the current state of the art for the most important aspects of UV emitters, their challenges and provides an outlook for future developments.

DOI： 10.1088/1361-6463/aba64c

Detailed analysis of Ga-rich current pathways created in an n-Al<inf>0.7</inf>Ga<inf>0.3</inf>N layer grown on an AlN template with dense macrosteps

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

Applied Physics Express 13 巻 ( 12 ) 頁： 124001 2020年12月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

To clarify the behavior of the AlGaN in 20 nm wide Ga-rich current pathways in an n-AlGaN layer, which assists carrier localization in AlGaN-based light-emitting diodes, we performed a detailed analysis using an n-Al0.7Ga0.3N layer on AlN with dense macrosteps on a 1.0 miscut sapphire substrate. Energy-dispersive X-ray spectra, obtained using cross-sectional scanning transmission electron microscopy calibrated by Rutherford backscattering and cross-sectional cathodoluminescence spectra, indicated that AlN mole fraction in the Ga-rich current pathways was nearly ∼2/3. This result is consistent with those of other research groups, suggesting that metastable Al2/3Ga1/3N is created in Ga-rich current pathways.

DOI： 10.35848/1882-0786/abcb49

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

Seong, TY; Amano, H

SURFACES AND INTERFACES 21 巻頁： 100765 2020年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Surfaces and Interfaces

III-V compound semiconductor-based light emitting devices (LEDs) operating in ultraviolet to visible wavelength ranges are greatly important for their applications, including displays, solid-state lighting, biomedical applications, optogenetics, and high bandwidth visible light communications. The performance of such LEDs is unavoidably affected by the surface characteristics of semiconductor layers. In particular, for LEDs, plasma-etching processes are inevitably adopted to define mesas, via holes and waveguides. The presence of surface defects is exceedingly detrimental to the device performance. It is therefore vital to understand the passivation mechanisms and approaches in order to control and so to maximize the efficiency. Here, we review recent progress in the surface treatment and passivation of III-V compound semiconductors-based LEDs. We show how different types of passivation approaches, including treatments with aqueous solutions, dielectric materials, or combination of both, affect the surface states and plasma-induced defects and hence the electrical and optical performance of LEDs.

DOI： 10.1016/j.surfin.2020.100765

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

Evropeitsev, EA; Kazanov, DR; Robin, Y; Smirnov, AN; Eliseyev, IA; Davydov, VY; Toropov, AA; Nitta, S; Shubina, TV; Amano, H

SCIENTIFIC REPORTS 10 巻 ( 1 ) 頁： 19048 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

Core–shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) are promising for monolithic white light-emitting diodes and multi-color displays. Such applications, however, are still a challenge because intensity of the red band is too weak compared with blue and green. To clarify this problem, we measured photoluminescence of different NRs, depending on power and temperature, as well as with time resolution. These studies have shown that dominant emission bands come from nonpolar and semipolar QWs, while a broad yellow-red band arises mainly from defects in the GaN core. An emission from polar QWs located at the NR tip is indistinguishable against the background of defect-related luminescence. Our calculations of electromagnetic field distribution inside the NRs show a low density of photon states at the tip, which additionally suppresses the radiation of polar QWs. We propose placing polar QWs inside a cylindrical part of the core, where the density of photon states is higher and the well area is much larger. Such a hybrid design, in which the excess of blue radiation from shell QWs is converted to red radiation in core wells, can help solve the urgent problem of red light for many applications of NRs.

DOI： 10.1038/s41598-020-76042-0

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

Piva, F; De Santi, C; Deki, M; Kushimoto, M; Amano, H; Tomozawa, H; Shibata, N; Meneghesso, G; Zanoni, E; Meneghini, M

PHOTONICS RESEARCH 8 巻 ( 11 ) 頁： 1786 - 1791 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Photonics Research

In this work, we analyze and model the effect of a constant current stress on an ultraviolet light-emitting diode with a nominal wavelength of 285 nm. By carrying out electrical, optical, spectral, and steady-state photocapacitance (SSPC) analysis during stress, we demonstrate the presence of two different degradation mechanisms. The first one occurs in the first 1000 min of stress, is ascribed to the decrease in the injection efficiency, and is modeled by considering the defect generation dynamics related to the de-hydrogenation of gallium vacancies, according to a system of three differential equations; the second one occurs after 1000 min of stress and is correlated with the generation of mid-gap defects, for which we have found evidence in the SSPC measurements. Specifically, we detected the presence of deep-level states (at 1.6 eV) and mid-gap states (at 2.15 eV), indicating that stress induces the generation of non-radiative recombination centers.

DOI： 10.1364/PRJ.401785

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

Robin, Y; Bournet, Q; Avit, G; Pristovsek, M; André, Y; Trassoudaine, A; Amano, H

SEMICONDUCTOR SCIENCE AND TECHNOLOGY 35 巻 ( 11 ) 頁： 115005 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Semiconductor Science and Technology

We show evidence that tunnel junctions (TJs) in GaN grown by metal-organic vapor phase epitaxy are dominated by defect level-assisted tunneling. This is in contrast with the common belief that highly doped layers (>1020 cm−3) are required to narrow the TJ space charge region and promote the band-to-band tunneling. Our conclusion stems from the study and the review of the major doping limitations of carefully optimized p++ and n++ layers. The secondary ions mass spectroscopy profiles of GaN based TJ LEDs show a strong oxygen concentration located close to the p++/n++ interface, typical for three dimensional growth. In addition, considering the doping limitation asymmetry and Mg carry-over, our simulations indicate a depletion region of more than 10 nm which is buried in a rough and defective n++ layer. However, decent electrical characteristics of the studied TJ based LEDs are obtained, with a low penalty voltage of 1.1 V and a specific differential resistance of about 10-2 Ω.cm2 at 20 mA. This indicates that a common TJ could be greatly optimized by using a moderate doping (∼1019 cm−3) while intentionally introducing local defects within the TJ.

DOI： 10.1088/1361-6641/abad73

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

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

ACS APPLIED MATERIALS & INTERFACES 12 巻 ( 41 ) 頁： 46466 - 46475 2020年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS applied materials & interfaces

Hexagonal boron nitride (hBN) and diamond are promising materials for next-generation electronics and optoelectronics. However, their combination is rarely reported. In this study, we for the first time demonstrate the success to direct growth of two-dimensional (2D) hBN crystal layers on diamond substrates by metalorganic vapor phase epitaxy. Compared with the disordered growth we found on diamond (100), atomic force microscopy, X-ray diffraction, and transmission electron microscopy results all support 2D hBN with highly oriented lattice formation on diamond (111). Also, the epitaxial relationship between hBN and diamond (111) substrate is revealed to be [0 0 0 1]hBN // [1 1 1]diamond and [1 0 1̅ 0]hBN // [1 1 2̅]diamond. The valence band offset at hBN/diamond (111) heterointerface determined by X-ray photoelectron spectroscopy is 1.4 ± 0.2 eV, thus yielding a conduction band offset of 1.0 ± 0.2 eV and type II staggered band alignment with a bandgap of 5.9 eV assumed for hBN. Furthermore, prior thermal cleaning of diamond in a pure H2 atmosphere smoothens the surface for well-ordered layered hBN epitaxy, while thermal cleaning in a mixed H2 and NH3 atmosphere etches the diamond surface, creating many small faceted pits that destroy the following epitaxy of hBN.

DOI： 10.1021/acsami.0c11883

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

Zhang, ZY; Kushimoto, M; Horita, M; Sugiyama, N; Schowalter, LJ; Sasaoka, C; Amano, H

APPLIED PHYSICS LETTERS 117 巻 ( 15 ) 頁： 152104 2020年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

The space charge density profile of the nondoped AlGaN-based p-type cladding layer for UV-C laser diodes realized by distributed polarization doping is examined theoretically and experimentally. The analysis of the capacitance-voltage measurement revealed that the average effective acceptor density of 4.2×1017 cm-3 is achieved even without impurity doping, and it is in good agreement with the theoretical prediction from the measured Al composition profile. This result suggests that the cladding layer is ideal for UV-C LDs because it provides sufficient hole injection while potentially avoiding internal losses due to impurity doping.

DOI： 10.1063/5.0027789

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