Toru Nagashima

Tokuyama (Japan)

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Yoshinao Kumagai

Tokyo University of Agriculture and Technology

Akinori Koukitu

Tokyo University of Agriculture and Technology

Reo Yamamoto

Tokuyama (Japan)

Zlatko Sitar

North Carolina State University

Ramón Collazo

North Carolina State University

Toru Kinoshita

The Memory Clinic

Rafael Dalmau

HexaTech (United States)

Ken Goto

Tokyo University of Agriculture and Technology

Hisashi Murakami

Tokyo University of Agriculture and Technology

R. Schlesser

HexaTech (United States)

Cooperative Institutions

Tokuyama (Japan)

Tokyo University of Agriculture and Technology

North Carolina State University

Adroit Materials (United States)

Tokyo Institute of Technology

Kyoto University

The University of Tokyo

National Institute of Information and Communications Technology

University of Tsukuba

HexaTech (United States)

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Vacancy compensation and related donor-acceptor pair recombination in bulk AlN

Applied Physics Letters (2013)

Benjamin E. Gaddy Zachary Bryan Isaac Bryan Ronny Kirste Jinqiao Xie

A prominent 2.8 eV emission peak is identified in bulk AlN substrates grown by physical vapor transport. This peak is shown to be related to the carbon concentration in the samples. Density functional theory calculations predict that this emission is caused by a donor-acceptor pair (DAP) recombination between substitutional carbon on the nitrogen site and a nitrogen vacancy. Photoluminescence and photoluminescence-excitation spectroscopy are used to confirm the model and indicate the DAP character of the emission. The interaction between defects provides a pathway to creating ultraviolet-transparent AlN substrates for optoelectronics applications.

Acceptor

Carbon fibers

Wide-bandgap semiconductor

Ultraviolet

10.1063/1.4824731

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Citations (88)

High-speed epitaxial growth of AlN above by hydride vapor phase epitaxy

Journal of Crystal Growth (2007)

Toru Nagashima Manabu Harada Hiroyuki Yanagi Yoshinao Kumagai Akinori Koukitu

Susceptor

Atmospheric temperature range

Vapor phase

10.1016/j.jcrysgro.2006.10.260

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Citations (39)

Stimulated emission mechanism of aluminum nitride

Physical review. B./Physical review. B (2022)

Ryota Ishii Toru Nagashima Reo Yamamoto Tatsuya Hitomi Mitsuru Funato

Photoluminescence and stimulated emission spectroscopies were performed on transparent aluminum nitride (AlN) substrates grown by hydride vapor-phase epitaxy. The stimulated emission was observed from cryogenic to room temperatures and its origin was assigned on the basis of the spontaneous emission spectra and existing theories. Two stimulated emission mechanism crossovers were also found. One was a temperature-induced crossover from a purely excitonic mechanism to a carrier-involved mechanism, which is a universal behavior in semiconducting materials. The other was an excitation-power--induced crossover from an exciton--exciton scattering mechanism to a phonon-mediated mechanism, which is a unique behavior attributed to the peculiar excitonic structure (negative crystal-field splitting and positive electron--hole exchange interaction energies) of AlN.

10.1103/physrevb.105.205206

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Citations (8)

XFEM/CZM結合アプローチを用いた複合積層板における進行性損傷と破壊の数値シミュレーション【Powered by NICT】

Composites Part A Applied Science and Manufacturing (2017)

R. Higuchi Tomonaga Okabe Toru Nagashima

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Evaluation of Threading Dislocation Densities in HVPE-Grown AlN Substrates by Wet Chemical Etching

The Japan Society of Applied Physics (2017)

Mari Higuchi Taro Mitsui Toru Nagashima Reo Yamamoto Keita Konishi

Threading (protein sequence)

Isotropic etching

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Formation Behavior of Infrared Light Scattering Defects in Silicon during Czochralski Crystal Growth

Journal of The Electrochemical Society (1995)

Masataka Hourai Toru Nagashima Eiji Kajita Shinitirou Miki Tatsuhiko Shigematsu

The formation behavior of grown‐in defects which are considered to be oxygen precipitates formed during CZ‐Si crystal growth, was investigated by means of infrared light scattering tomography. The following results were obtained. (i) The density of the IR light scattering defects decreases with a reduction in the crystal pulling rate. (ii) The defects are not formed just after solidification, but they grow to a size detectable by LST during cooling to about 1100°C. (iii) The defect density decreases by slow cooling in the temperature range from to 1500 to 1000°C, while their size increases. The formation mechanism of the defects was qualitatively discussed from the point of view of the interaction between oxygen atoms and point defects by a consideration of the free energy change and the critical radii of nuclei for oxygen precipitation. It was suggested that the formation of the defects depends on the vacancy concentration. In the case of a constant vacancy concentration, their density and size are determined by the cooling rate in the temperature range from 1150 to 1000°C.

Crystal (programming language)

Atmospheric temperature range

Scattering rate

10.1149/1.2048712

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Citations (29)

Influence of NH 3 partial pressure on homoepitaxial growth of AlN by HVPE

The Japan Society of Applied Physics (2019)

Nao Takekawa Daichi Saito Yudai Shimizu Ken Goto Toru Nagashima

Partial pressure

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Study of Dislocations in Homoepitaxially and Heteroepitaxially Grown AlN Layers

physica status solidi (a) (2020)

Ken Goto Nao Takekawa Toru Nagashima Reo Yamamoto Г. Позина

Dislocation densities in AlN layers grown on c ‐plane sapphire and physical vapor transport‐grown AlN (PVT‐AlN) (0001) substrates, by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE), respectively, are evaluated from the density of etch pits formed in sodium hydroxide (NaOH)/potassium hydroxide (KOH) eutectic heated to 450 °C. In the heteroepitaxial layers grown by MOVPE on the sapphire substrates, etch pits with different sizes are formed. Cross‐sectional transmission electron microscopy (TEM) observations reveal that the large, medium, and small pits, with densities of 1.4 × 10 6 , 2.6 × 10 7 , and 6.9 × 10 9 cm −2 , respectively, correspond to screw, mixed, and edge dislocations, respectively. In contrast, in the homoepitaxial layers grown by HVPE on the PVT‐AlN substrates, only one kind of etch pit with uniform size corresponding to the edge dislocations is formed with a density of 10 3 –10 4 cm −2 . Cross‐sectional TEM observation confirms that the edge dislocations in the homoepitaxial layer propagate from the substrate through the interface, which indicates that the dislocation density does not increase during homoepitaxial growth by HVPE. The HVPE‐AlN homoepitaxial layers grown on the PVT‐AlN substrates are found to have very low dislocation density.

Etch pit density

10.1002/pssa.202000465

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Citations (4)

Forecast of Japanese Fiber Industry

Sen i Gakkaishi (2006)

Toru Nagashima

10.2115/fiber.62.p_285

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On the origin of the 265 nm absorption band in AlN bulk crystals

Applied Physics Letters (2012)

Ramón Collazo Jinqiao Xie Benjamin E. Gaddy Zachary Bryan Ronny Kirste

Single crystal AlN provides a native substrate for Al-rich AlGaN that is needed for the development of efficient deep ultraviolet light emitting and laser diodes. An absorption band centered around 4.7 eV (∼265 nm) with an absorption coefficient above 1000 cm−1 is observed in these substrates. Based on density functional theory calculations, substitutional carbon on the nitrogen site introduces absorption at this energy. A series of single crystalline wafers were used to demonstrate that this absorption band linearly increased with carbon, strongly supporting the model that CN- is the predominant state for carbon in AlN.

Carbon fibers

Crystal (programming language)

Absorption band

10.1063/1.4717623

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Citations (148)