研究者詳細 - 天野　浩

Localization and transient emission properties in InGaN/GaN quantum wells of different polarities within core- shell nanorods

PubMed

Robin, Y; Evropeitsev, EA; Shubina, TV; Kirilenko, DA; Davydov, VY; Smirnov, AN; Toropov, AA; Eliseyev, IA; Bae, SY; Kushimoto, M; Nitta, S; Ivanov, SV; Amano, H

NANOSCALE 11 巻 ( 1 ) 頁： 193 - 199 2019年1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：Nanoscale

Transient photoluminescence (PL) characteristics and localization phenomena in InGaN/GaN core-shell nanorods (NRs) were investigated from 6 K up to 285 K. The NRs exhibit three well-defined PL bands in the near-UV, blue, and green range ascribed to the emission of quantum well (QW) areas situated at the (1.00) sidewalls, (10.1) top facets, and (00.1) tip, respectively. At low temperature, time-resolved PL shows a fast decay time of about 0.5 ns for the semi- and non-polar QWs, while the polar QWs exhibit at least a twice-longer time. Rapid delocalization of carriers above 50 K indicates shallow potential fluctuations in the QWs. At room temperature, the characteristic fast PL decay time of the three QW bands stabilizes around 300 ps. The slow decaying PL components have different characteristic decay times that are explained by additional localization at basal stacking faults (BSFs), taking into account the quantum confined Stark effect. In addition, narrow excitonic luminescence lines are observed in the BSF-enriched polar QWs, providing direct evidence of the impact of the BSF/QW crossings on the optical properties of the NRs. A PL rise time of about 100 ps does not show any deviation between bands. These findings are suggestive of similar transport mechanisms in temperature equilibrium without inter-facet transport between different QWs. We believe that predictable transient characteristics can play a key role in creating uniform NR ensembles for device applications.

DOI： 10.1039/c8nr05863f

Carrier localization structure combined with current micropaths in AlGaN quantum wells grown on an AlN template with macrosteps

PubMed

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

Applied Physics Letters 114 巻 ( 1 ) 頁： 011102 2019年1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 Letters

The microscopic structural and optical characteristics of AlGaN-based light-emitting diodes grown on AlN templates with macrosteps were evaluated. Cross-sectional transmission electron microscopy in the high-angle annular dark field scanning mode and microscopic energy dispersive X-ray spectroscopy reveal that the AlGaN cladding layer under the AlGaN quantum wells (QWs) has microscopic compositional modulations originating from the macrosteps at the AlN template surface. The Ga-rich oblique zones in the cladding layer likely behave as current micropaths. These micropaths are connected to the carrier localization structure, which is formed by the modulation of both the well widths and the compositions of the QWs. In-plane spatially-resolved cathodoluminescence (CL) spectroscopy indicated significant inhomogeneity of the CL characteristics: the brighter emission with a lower peak photon energy confirms the existence of the carrier localization structure in the QWs. Carrier localization in the QWs along with the current micropaths in the AlGaN cladding layer appears to increase the external quantum efficiency of AlGaN LEDs.

DOI： 10.1063/1.5063735

286 nm monolithic multicomponent system

Yuan, JL; Jiang, Y; Shi, Z; Gao, XM; Wang, YJ; Sun, XJ; Li, DB; Liu, YH; Amano, H

JAPANESE JOURNAL OF APPLIED PHYSICS 58 巻 ( 1 ) 頁： 010909 2019年1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：Japanese Journal of Applied Physics

We present a 286 nm monolithic multicomponent system in which two identical multiple quantum well (MQW) diodes merge with a waveguide together on a single chip. The monolithic multicomponent system allows all existing standard fabrication processes and establishes an optical link between two MQW-diodes because of the simultaneous emission-detection phenomenon. One MQW-diode transcribes electronic information into an optical signal to be coupled into a waveguide. The guided light then propagates along the waveguide to the other MQW-diode that converts the optical signal into an electronic one. A spatial light transmission at 50 Mbps is demonstrated using non-return-to-zero on-off keying modulation.

DOI： 10.7567/1347-4065/aaf3aa

Electronic structure analysis of core structures of threading dislocations in GaN

Nakano, T; Chokawa, K; Araidai, M; Shiraishi, K; Oshiyama, A; Kusaba, A; Kangawa, Y; Tanaka, A; Honda, Y; Amano, H

2019 COMPOUND SEMICONDUCTOR WEEK (CSW) 頁： . 2019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：2019 Compound Semiconductor Week, CSW 2019 - Proceedings

It is known that threading dislocations degrade the performance of GaN-based electronic devices. Electronic structure of threading dislocations in GaN is not fully understood. Accordingly, we examine the electronic structures of threading dislocations in GaN using first principles calculations based on density functional theory (DFT) and to clarify the origin of the leakage current. We have comprehensively studied the relation between threading core structures and electronic property in GaN thin films. Our calculation models of threading dislocations are the edge dislocations with Burgers vectors of 1/3 [11-20] and the screw dislocations with Burgers vectors of [0001]. We examined various core types of the threading dislocations. We found that both edge dislocations and screw dislocations do not cause the leakage currents in n-type GaN based devices because no defect level appears near the conduction band bottom.

DOI： 10.1109/iciprm.2019.8819270

Light-Emitting Diodes Materials, Processes, Devices and Applications Foreword

Amano, H

LIGHT-EMITTING DIODES: MATERIALS, PROCESSES, DEVICES AND APPLICATIONS 4 巻頁： V - V 2019年

MOVPE growth and high-temperature annealing of (10(1)over-bar0) AlN layers on (10(1)over-bar0) sapphire

Dinh Duc V., Amano Hiroshi, Pristovsek Markus

JOURNAL OF CRYSTAL GROWTH 502 巻頁： 14-18 2018年11月

What is red? On the chromaticity of orange-red InGaN/GaN based LEDs

Robin, Y; Pristovsek, M; Amano, H; Oehler, F; Oliver, RA; Humphreys, CJ

JOURNAL OF APPLIED PHYSICS 124 巻 ( 18 ) 頁： 183102 2018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：Journal of Applied Physics

The full width at half maximum (FWHM) of the luminescence of visible InGaN quantum well (QW) based emitters increases with wavelength. This broadening of the luminescence decreases the color saturation from 100% to about 70% up a wavelength shorter than 515 nm. For emission wavelengths longer than 515 nm, the saturation surprisingly increases again and reaches 95% beyond 560 nm. More important, in the yellow-red range, the perceived hue is strongly blue-shifted by a broad emission. This phenomenon is known as Abney effect, and it originates from the spectral sensitivities of the cone cells of the human eyes. As a consequence, for red InGaN QW based LEDs, the peak wavelength must be even further in the red. Based on a large set of QWs grown on different crystal orientations, we correlated the wavelength and the luminescence FWHM of InGaN/GaN QWs to build a model which predicts the perceived chromaticity, i.e., the apparent hue and saturation of yellow-red nitride LEDs. We also applied this model to (11-22), a-plane, and m-plane QWs and compared our data to the state-of-the-art of the literature. We concluded that the FWHM of the luminescence is a critical parameter to design and a further challenge for red InGaN-based light-emitting diodes.

DOI： 10.1063/1.5047240

Simultaneous Growth of Various InGaN/GaN Core-Shell Microstructures for Color Tunable Device Applications

Robin, Y; Liao, YQ; Pristovsek, M; Amano, H

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 215 巻 ( 21 ) 頁： 1800361 2018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：Physica Status Solidi (A) Applications and Materials Science

An approach to simultaneously grow independent core-shell structures emitting at different wavelengths by selective area epitaxy is presented. By using seeds of different sizes, the monolithic integration of various GaN crystals including elongated nano-rods (NRs), micro-platelets (MPs), and a range of pyramid-like structures are demonstrated. Dominant non-polar sidewalls cover more than 75% of the surface area of the NRs, while the polar top facet are about 80% of the total surface of the MPs. InGaN/GaN quantum wells (QWs) deposited on these structures exhibit independent and well-separated emissions in the green–blue and orange–red ranges, respectively. The pyramid-like structures at intermediate seed sizes are more complex with semi-polar facets nearly totaling 60% of the total surface area, resulting in yellow luminescence strongly broadened by the nearby facets contributions. These results suggest the total surface area of each facets and the resulting optical properties of the crystals can be tailored by adjusting the size of the seeds. However, further improvements are required to locally enhance the vertical, pyramidal, and lateral growth of the GaN cores and increase the spectral purity of the different QWs. The approach presented is of interest to design multi-wavelength devices which requires independent subpixels of high color purity.

DOI： 10.1002/pssa.201800361

Analysis of negative electron affinity InGaN photocathode by temperature-programed desorption method

Kashima, M; Sato, D; Koizumi, A; Nishitani, T; Honda, Y; Amano, H; Iijima, H; Meguro, T

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 36 巻 ( 6 ) 頁： 06JK02 2018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：Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics

A III-V semiconductor with a few monolayers of alkali metals (e.g., Cs) forms a negative electron affinity (NEA) surface, for which the vacuum level lies below the conduction band minimum of the base semiconductor. The photocathodes that form an NEA surface (NEA photocathodes) have various advantages, such as low emittance, a large current, high spin polarization, and ultrashort pulsed operation. The NEA-InGaN photocathode, which is sensitive to blue light, has been studied as a material for the next-generation robust photocathode. However, the proper conditions for forming NEA surfaces remain unknown. The authors consider whether the suitable process for NEA surfaces can be understood by investigating the relationship between the electron emission and the adsorption state of alkali metals. In this study, the relationship between the electron emission and the adsorption state of Cs on the p-type InGaN (0001) was analyzed by the temperature-programed desorption (TPD) method using a quadrupole mass spectrometer. From the results of the TPD measurements, it was shown that there were several adsorption states of Cs on InGaN. The quantum efficiency (QE), which indicates the ratio of emitted electrons to incident photons, increased while Cs desorption occurred. The authors divided the formation process of an NEA surface into several sections to investigate the adsorption states of Cs related to the electron emission and to discuss the reasons why the QE increased despite the desorbed Cs. From the results of the NEA activation in each section, it was shown that there were sections where the QE increased by reacting with O2 after Cs supply stopped. There is a possibility that several layers reacting with O2 and those not reacting with O2 are formed by performing NEA activation until the QE saturates. From the results of the TPD measurements in each section, it was suggested that there was a Cs peak at above 700 °C when the TPD method was carried out immediately after confirming the electron emission. Therefore, the adsorption state of Cs that formed a peak at above 700 °C had a close relation to the electron emission. It is considered that the increase of the QE in the TPD was affected by adsorbed Cs compounds that reacted with O2. Although the mechanism is not understood, it is known that the QE was increased by the reaction of Cs adsorbed compounds and O2 in previous studies. It was suspected that layers that reacted with O2 appeared from TPD and then the QE increased by reacting with O2.

DOI： 10.1116/1.5048061

Crystal engineering by tuning the growth kinetics of GaN 3-D microstructures in SAG-HVPE

Full-duplex light communication with a monolithic multicomponent system

Wang Yongjin, Wang Xin, Zhu Bingcheng, Shi Zheng, Yuan Jialei, Gao Xumin, Liu Yuhuai, Sun Xiaojuan, Li Dabing, Amano Hiroshi

LIGHT-SCIENCE & APPLICATIONS 7 巻頁： 83 2018年10月

Avit Geoffrey, Zeghouane Mohammed, Andre Yamina, Castelluci Dominique, Gil Evelyne, Bae Si-Young, Amano Hiroshi, Trassoudaine Agnes

CRYSTENGCOMM 20 巻 ( 40 ) 頁： 6207 - 6213 2018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：CrystEngComm

The growth of GaN 3-D microstructures is investigated by SAG-HVPE. Capitalizing on the properties of this kinetically-controlled process, the main experimental parameters and physical mechanisms that control the shaping of 3D GaN prisms and pyramids in SAG-HVPE are highlighted. Growth experiments performed on N-polar AlN/Si(100) and Ga-polar GaN/Si(111) substrates also provide insight into how to switch from a pyramid to a prismatic shape for a given substrate polarity. The aspect ratio of GaN rods could be tuned by playing with the HCl partial pressure additionally introduced during growth. The influence of both mass transport and surface kinetics is discussed, as the crystal growth rate varies with increasing surface area as time goes by. Ammonia treatment prior to the growth, aimed at blocking the r planes thanks to H2 passivation, is proposed to tune the morphology of the GaN rods. Raman spectroscopy performed on individual GaN rods shows no relevant strain field and no structural differences between the rods and state-of-the-art bulk GaN.

DOI： 10.1039/c8ce01177j

Reduction of Residual Impurities in Homoepitaxial m-Plane (10(1)over-bar0) GaN by Using N-2 Carrier Gas in Metalorganic Vapor Phase Epitaxy

Comparing high-purity c- and m-plane GaN layers for Schottky barrier diodes grown homoepitaxially by metalorganic vapor phase epitaxy

Nagamatsu Kentaro, Ando Yuto, Ye Zheng, Barry Ousmane, Tanaka Atsushi, Deki Manato, Nitta Shugo, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS 57 巻 ( 10 ) 頁： 105501 2018年10月

High-temperature thermal annealing of nonpolar (10(1)over-bar0) AlN layers sputtered on (1 0(1)over-bar0) sapphire

Dinh Duc V, Hu Nan, Honda Yoshio, Amano Hiroshi, Pristovsek Markus

JOURNAL OF CRYSTAL GROWTH 498 巻頁： 377-380 2018年9月

「材料研究の楽しさ」

天野浩

表面と真空 61 巻 ( 9 ) 頁： 565 - 567 2018年9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：公益社団法人日本表面真空学会

半導体の王者は言わずと知れたSiである。市場規模を比べると，化合物半導体全部含めてもSiの1/10にも満たない。それでも化合物半導体，とりわけGaN系窒化物半導体にこだわっている理由は，この材料の物性自体がとても興味深いこと，およびSiでは出来ないことが出来る，或いは今後できそうだからである。本寄稿では，筆者が学生の頃からこれまで30年以上もの間取り組んでいるGaN系窒化物半導体材料の研究で，特に表面と真空について学んだことを中心に書かせて頂くことにする。

DOI： 10.1380/vss.61.565

CiNii Research

Detailed study of effects of duration of pre-AIN-growth trimethylaluminum step on morphologies of GaN layers grown on silicon substrate by metal organic chemical vapor deposition

Matsumoto Koji, Ono Toshiaki, Honda Yoshio, Murakami Satoshi, Kushimoto Maki, Amano Hiroshi

JAPANESE JOURNAL OF APPLIED PHYSICS 57 巻 ( 9 ) 頁： 091001 2018年9月

Barry Ousmane I., Lekhal Kaddour, Bae Si-Young, Lee Ho-Jun, Pristovsek Markus, Honda Yoshio, Amano Hiroshi

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 12 巻 ( 8 ) 頁： 1800124 2018年8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：Physica Status Solidi - Rapid Research Letters

The reduction of unintentional impurities in m-plane (1010) GaN homoepitaxial layers is demonstrated by using nitrogen (N2), as opposed to hydrogen (H2), as carrier gas in metalorganic vapor phase epitaxy (MOVPE). Secondary ion mass spectrometry (SIMS) analysis shows that the impurity levels of residual oxygen (O), carbon (C), and silicon (Si) are decreased by nearly one order of magnitude in N2-grown samples. Although the full width at half maximum (FWHM) values for the on-axis m-plane X-ray rocking curves of all specimens are quite similar (around 50 arcsec), plan-view scanning transmission electron microscopy (STEM) measurements reveal a clear reduction of dislocation densities in N2-grown films. Their origin is likely related to an initial surface roughening with H2 carrier gas, which also causes surface faceting resulting in the formation of large four-sided pyramidal hillocks, while using N2 results in smoother surfaces. Hence, MOVPE growth with N2 carrier gas is an effective method to lower the impurity incorporation in m-plane GaN materials in addition to reducing the formation of defects and improving the surface morphology, which can enable the development of high-performance GaN-based devices on non-polar surfaces.

DOI： 10.1002/pssr.201800124

Improvement of breakdown voltage of vertical GaN p-n junction diode with Ga<sub>2</sub>O<sub>3</sub> passivated by sputtering

Ueoka, Y; Deki, M; Honda, Y; Amano, H

JAPANESE JOURNAL OF APPLIED PHYSICS 57 巻 ( 7 ) 頁： 070302 2018年7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：Japanese Journal of Applied Physics

This article describes a new passivation process of Ga2O3, which consists by sputtering, for a vertical GaN p-n junction diode on a free-standing GaN substrate with a field-plate (FP) structure. We demonstrated reduced plasma damage during the sputtering process by cure annealing, and succeeded in improving the breakdown voltage (VB) to -550V with the FP, compared with VB of -200V without the FP. Ga2O3 is a suitable material for the FP because its dielectric constant is similar to that of GaN and it is more easily etched than Al2O3, which is used as a conventional insulator.

DOI： 10.7567/JJAP.57.070302

Study on the Main-Chain Structure of Amorphous Fluorine Resins for Encapsulating AlGaN-Based DUV-LEDs

Yamada, K; Nagasawa, Y; Nagai, S; Hirano, A; Ippommatsu, M; Aosaki, K; Honda, Y; Amano, H; Akasaki, I

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 215 巻 ( 10 ) 頁： 1700525 2018年5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：Physica Status Solidi (A) Applications and Materials Science

The main chain structure of optically isotropic amorphous fluorine resin for encapsulating AlGaN-based deep-ultraviolet LEDs (λ < 300 nm) is studied. One type of amorphous fluorine resin has a five-membered ring with a single oxygen atom and the other has that one with two oxygen atoms. Reliability testing is performed using AlGaN-based LEDs of 262 and 289 nm. For the resin with two oxygen atoms in the ring, visible damage to the electrode and significantly increased leakage current are considered to been caused by the photolysis of the ring induced by irradiation with deep-ultraviolet light. In contrast, electrode damage and increased leakage are not observed in the case of the resin with the single-oxygen ring.

DOI： 10.1002/pssa.201700525