Hiroya Kimura

Preparation of Large Freestanding GaN Substrates by Hydride Vapor Phase Epitaxy Using GaAs as a Starting Substrate

A freestanding GaN substrate over 2 inches in size was successfully prepared for the first time by hydride vapor phase epitaxy (HVPE) using GaAs as a starting substrate. In the experiment, a GaAs (111)A substrate with a SiO2 mask pattern on its surface was used. A thick GaN layer was grown on the GaAs substrate at 1030°C through the openings in the SiO2 mask. By dissolving the GaAs substrate in aqua regia, a freestanding GaN substrate about 500 µm thick was obtained. The full-width at half maximum (FWHM) in the ω-mode X-ray diffraction (XRD) profile of GaN (0002) plane was 106 arcsec. The dislocation density of the GaN substrate obtained was determined to be as low as 2×105 cm-2 by plan-view transmission electron microscopy (TEM). Hall measurements revealed the n-type conductivity of the GaN substrate with typical carrier concentration and carrier mobility of 5×1018 cm-3 and 170 cm2V-1s-1, respectively.

Preparation of large GaN substrates

Abstract A freestanding GaN substrate of over 2-in. size with low dislocation density was prepared by hydride vapor phase epitaxy (HVPE) using GaAs (111)A as a starting substrate. A SiO 2 mask pattern with round openings was formed directly onto the GaAs (111)A substrate. Then, a thick GaN layer was grown with numerous large hexagonal inverse-pyramidal pits constructed mainly by {11–22} facets maintained on the surface. After removing the GaAs substrate and subsequent lapping and polishing, a freestanding GaN about 500 μm in thickness was obtained. Etch pit observation reveals that etch pit groups with etch pit density 2×10 8 cm −2 at the center exist in the matrix area with etch pit density as low as 5×10 5 cm −2 . This distribution is due to the effect of large hexagonal pits on collecting dislocations at the bottom of the hexagonal pit. Dislocations propagate into the bottom of the pit mainly in the 〈11–20〉 or 〈1–100〉 direction parallel to (0001).

Si-doping in GaAs grown by metalorganic vapor phase epitaxy using tertiarybutylarsine and tetraethylsilane

Abstract We have developed a much safer metalorganic chemical vapor phase epitaxy (MOVPE) process with all liquid phase organic precursors without using hazardous gases including doping sources. In this study, the silicon doping in GaAs grown using tetraethylsilane with tertiarybutylarsine has been investigated. Excellent controllability and reproducibility of n-type doping level from 1 × 10 17 to 6 × 10 18 cm -3 with low carbon incorporation are confirmed. The carrier concentration increases with increasing growth temperature and decreases with increasing V/III ratio. In addition, we applied the MOVPE process with all liquid sources for the fabrication of the GaAs solar cell, and obtained good cell performance of over the conversion efficiency of 20%.