Halide vapor phase epitaxy of a thick c-plane α-Ga2O3 film on a high-quality α-Cr2O3/sapphire template

Abstract

α-Ga2O3 is a promising ultra-wide-bandgap semiconductor for future power devices, and the use of α-Cr2O3 buffer layers represents an effective approach to improve the crystalline quality of heteroepitaxial α-Ga2O3 films owing to the small lattice mismatch between the two materials. In this study, c-plane α-Ga2O3 films were grown using halide vapor phase epitaxy (HVPE) on high-quality α-Cr2O3/sapphire templates, and the dependence of crystalline quality on the film thickness was systematically investigated. HVPE growth was performed under atmospheric pressure at 520 °C using GaCl and O2 as the precursors and at a growth rate of 14 μm h−1. The film thickness was varied from 0.24 to 21 μm by controlling the growth time. X-ray 2θ–ω scan and pole figure measurements helped confirm that the α-Ga2O3 epilayers were phase-pure single-crystalline films. Thickness-dependent x-ray rocking curve measurements and reciprocal space mapping revealed that lattice relaxation began at a thickness of approximately 0.47 μm or less and virtually completed at thicknesses of 11 μm or greater. Cross-sectional scanning transmission electron microscopy results showed that dislocations were observed predominantly near the film surface and were absent at the α-Ga2O3/α-Cr2O3 interface. Etch-pit density measurements yielded a low dislocation density of 5.6 × 107 cm−2 for the fully strained 0.24 μm-thick film. The almost fully relaxed 21 μm-thick film showed a higher dislocation density of 3.9 × 108 cm−2. Nevertheless, this value was approximately one order of magnitude lower than that of an α-Ga2O3 film directly grown on a c-plane sapphire substrate under identical conditions.