Dr. Yohei Otoki Profile

Dr. Yohei Otoki

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Proceedings Article | 16 February 2017 Paper

Recent progress of high-quality GaN substrates by HVPE method

Hajime Fujikura, Takehiro Yoshida, Masatomo Shibata, Yohei Otoki

Proceedings Volume 10104, 1010403 (2017) https://doi.org/10.1117/12.2257202

KEYWORDS: Mass spectrometry, Gallium nitride, Epitaxy, Semiconducting wafers, Crystals, Silicon, Sapphire, Doping, Control systems, Material purity

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Recent progress in our hydride vapor-phase epitaxy (HVPE) technique is discussed. First, the void-assisted separation (VAS)-method for freestanding GaN fabrication is introduced and its recent progress is described. When conventional HVPE conditions are used in the VAS method, the reduction in threading dislocation density (TDD) stops when growth exceeds a certain critical thickness. This limitation was overcome by controlling the crystal hardness by appropriate HVPE conditions, resulting in GaN bulk crystals with the highest nanoindentation hardness value reported to date (22 GPa). Based on this, the TDD had been markedly reduced to the mid-10⁵/cm² range. With regard to the fabrication of large wafers, a 4" GaN substrate was successfully fabricated by using the VAS method. The hardness control was also found to be beneficial for fabrication of 4" GaN substrates with small off-angle variations. Additionally, we succeeded in fabricating a 7" GaN substrate by using a newly developed tiling method. With respect to the material purity, extremely pure GaN crystals were grown by using a quartz-free HVPE system. All impurity concentrations measured by secondary-ion mass spectrometry, including those of Si, O, and C, were below the detection limit. The high-purity layers displayed an insulating nature in the absence of a dopant; by Si doping, the electron concentration could be controlled over a wide range, down to 1 × 10¹⁵/cm³, with a high mobility of over 1100 cm²/Vs. This indicates that HVPE has potential applications as a tool for the epitaxial growth of power-device structures.

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