Structural defects and luminescence features in heteroepitaxial GaN grown on on-axis and misoriented substrates

The microstructure and luminescence properties of a series of GaN epilayers grown on sapphire and SiC substrates with various misorientations have been correlated to assess the origins of the luminescence features in the misoriented samples. Samples grown on 3.5° offcut SiC and 5° and 9° offcut sapphire substrates both exhibit photoluminescence peaks near ~3.2 and ~3.4 eV, which are absent in the on-axis SiC and sapphire cases. Transmission electron microscopy shows that the misoriented samples have configurations of I1 basal plane stacking faults, which fold into prismatic stacking faults with stair-rod dislocations at their intersections. The luminescence features are proposed to possibly arise from transitions involving the prismatic stacking faults andor the stair-rod dislocations associated with their mutual intersections and their intersections with the basal plane stacking faults.