Homoepitaxial Hydride Vapor Phase Epitaxy Growth on GaN Wafers Manufactured by the Na-Flux Method

Abstract

Homoepitaxial hydride vapor phase epitaxy (HVPE) growth on GaN substrates grown with a Na-flux method, which is the most promising approach for fabrication of large-diameter, low-dislocation-density, fast-growing GaN wafers, was attempted for the first time. We found that, when different growth methods are combined, the differences in oxygen concentrations between a seed and grown crystal must be eliminated to maintain the crystallographic quality of the seed. Two kinds of Na-flux-grown seed crystals were prepared; one had a surface composed of c, {101̅2}, and {101̅1} planes, the other a surface composed entirely of c-planes. Both crystals were sliced, ground, mirror-polished, and applied for 500-μm-thick HVPE growth. In the former sample, the seed crystal generated fine cracks, and the epitaxially grown layer had a rough surface and included many dislocations; the latter sample showed no fault. For clarifying the mechanism of crystal degradation, we investigated the lattice constants of each growth sector using an X-ray microbeam and found that lattice constants in the {101̅1}-growth sector were expanded compared to those in other growth sectors due to oxygen impurities. These values were estimated to be much larger than those of HVPE crystals, resulting in the crystal degradation after the HVPE growth by a lattice mismatch.