Measuring dislocation densities in nonpolar a-plane GaN films using atomic force microscopy

Dislocation densities in nonpolar GaN films were determined using atomic force microscopy (AFM) by counting pits in the GaN surface revealed by a SiH 4 surface treatment. This treatment increased the number of pits detected by a factor of 2 compared with the untreated surface. AFM and transmission electron microscopy analysis of a series of SiH 4 -treated calibration samples indicated that surface pit and dislocation densities corresponded well up to a dislocation density of ∼6 × 10 9 cm −2 , above which surface pit overlap meant that dislocation densities determined by AFM were underestimated. For all samples with dislocation densities below 6 × 10 9 cm −2 , spatial analysis of the surface pit positions showed that dislocations typically accumulated in bands at island coalescence boundaries.