Thin wurtzite films were grown, by plasma-enhanced molecular beam epitaxy, onto the basal plane of 6H-SiC; with or without an AlN buffer layer. Threading defects, which were identified (from high-resolution electron micrographs) to be double-positioning boundaries, originated at the substrate/buffer and/or buffer/film interfaces. The density of these faults seemed to be related to the smoothness of the substrate. Thus, their occurrence emphasized the need for proper substrate preparation. Stacking faults were often visible within the GaN, parallel to the SiC substrate basal plane, and sometimes terminating at the double-positioning boundaries. These faults were related to the particular growth conditions, with a greatly decreased density resulting from a lower plasma power during GaN deposition. The growth of high-quality GaN, without stacking faults, was achieved (without using an AlN buffer layer) by carrying out deposition directly onto a vicinal SiC surface with a mis-cut angle of 4. Such stepped substrates were suggested to be a potentially useful means for the controlled growth of double-positioning boundaries, which could then act as suitable stress-relieving defects; instead of misfit dislocations.

D.J.Smith, D.Chandrasekhar, B.Sverdlov, A.Botchkarev, A.Salvador, H.Morkoç: Applied Physics Letters, 1995, 67[13], 1830-2