Microscopic distribution of extended defects and blockage of threading dislocations by stacking faults in semipolar (11¯01) GaN revealed from spatially resolved luminescence

Abstract

Spatial distribution of extended defects in semipolar (11¯01)-oriented GaN layers grown on patterned (001) Si substrates with striped grooves of varying width was investigated by optical means only using near-field scanning optical microscopy (NSOM) and cathodoluminescence (CL). A high density of basal and prismatic stacking faults was observed in the c− wings, and the threading dislocations in c+ wings, which appear as dark patterns in the NSOM and CL images, were found to bend toward the surface during the initial stages of growth. In the case when growing c+ front of GaN made contact with the SiO2 masking layer during growth, stacking faults were found to form also in the c+ wings. These additional stacking faults effectively blocked propagation of dislocations along the c+ direction, resulting in high quality stripes virtually free of defects. As revealed by optical means only without the need for any structural investigation, such control over the threading dislocation density using select growth geometries is potentially advantageous for improving semipolar (11¯01)GaN.