alpha-Gallium Oxide Films on Microcavity-Embedded Sapphire Substrates Grown by Mist Chemical Vapor Deposition for High-Breakdown Voltage Schottky Diodes

Abstract

alpha-Gallium oxide, with its large band gap energy, is a promising material for utilization in power devices. Sapphire, which has the same crystal structure as alpha-Ga2O3, has been used as a substrate for alpha-Ga2O3 epitaxial growth. However, lattice and thermal expansion coefficient mismatches generate a high density of threading dislocations (TDs) and cracks in films. Here, we demonstrated the growth of alpha-Ga2O3 films with reduced TD density and residual stress on microcavity-embedded sapphire substrates (MESS). We fabricated the two types of substrates with microcavities: diameters of 1.5 and 2.2 mu m, respectively. We confirmed that round conical-shaped cavities with smaller diameters are beneficial for the lateral overgrowth of alpha-Ga2O3 crystals with lower TD densities by mist chemical vapor deposition. We could obtain crack-free high-crystallinity alpha-Ga2O3 films on MESS, while the direct growth on a bare sapphire substrate resulted in an alpha-Ga2O3 film with a number of cracks. TD densities of alpha-Ga2O3 films on MESS with 1.5 and 2.2 mu m cavities were measured to be 1.77 and 6.47 x 10(8) cm(-2), respectively. Furthermore, cavities in MESS were certified to mitigate the residual stress via the redshifted Raman peaks of alpha-Ga2O3 films. Finally, we fabricated Schottky diodes based on alpha-Ga2O3 films grown on MESS with 1.5 and 2.2 mu m cavities, which exhibited high breakdown voltages of 679 and 532 V, respectively. This research paves the way to fabricating Schottky diodes with high breakdown voltages based on high-quality alpha-Ga2O3 films.