Characterization of structural defects in wurtzite GaN grown on 6H SiC using plasma-enhanced molecular beam epitaxy

Thin wurtzite GaN films have been grown by plasma-enhanced molecular beam epitaxy on the basal plane of 6H SiC, with and without AlN buffer layers. Threading defects, identified from high-resolution electron micrographs as double-positioning boundaries (DPBs), originate at the substrate-buffer and/or buffer-film interfaces. The density of these faults seems to be related to the smoothness of the substrate, so that their occurrence emphasizes the importance of adequate substrate preparation. Stacking faults within the GaN are often visible parallel to the SiC substrate basal plane, sometimes terminating at the DPBs. These faults are related to the particular growth conditions, with greatly decreased density obtained for lower plasma power during GaN deposition. Growth of high quality GaN without stacking faults was achieved without using AlN buffer layers by deposition directly onto a vicinal SiC surface having a miscut angle of 4°. Such stepped substrates represent a potentially useful means for controlled growth of the DPBs, which could then serve as suitable stress-relieving defects in lieu of misfit dislocations.