Surface etching of 6H-SiC (0001) and surface morphology of the subsequently grown GaN via MOCVD

The correlation between surface morphological properties of the GaN epilayers and the surface conditions of 6H-SiC (0001) substrates etched in H-2, C2H4/H-2, and HCl/H-2 was studied. Etching 6H-SiC in H-2 produced a high quality surface with steps and terraces, while etching in HCl/H-2 produced either a rough surface with many pits and hillocks or a smooth surface similar to that etched in H-2, depending on the HCl concentration and temperature. The GaN epilayers were subsequently deposited on these etched substrates using either a low temperature GaN or a high temperature AlN buffer layer via MOCVD. The substrate surface defects increased the density and size of the "giant" pinholes (2-4 mu m) on GaN epilayers grown on a LT-GaN buffer layer. Small pinholes (<100 nm) were frequently observed on the samples grown on a HT-AlN buffer layer, and their density decreased with the improved surface quality. The non-uniform GaN nucleation caused by substrate surface defects and the slow growth rate of {1 (1) over bar 01} planes of the islands were responsible for the formation of "giant" pinholes, while the small pinholes were believed to be caused by misfit dislocations.