Dislocation densities in non-polar GaN films were determined by using atomic force microscopy and counting pits in the GaN surface revealed by a SiH4 surface treatment. This treatment increased the number of pits detected by a factor of 2, as compared with the untreated surface. Atomic force microscopy and transmission electron microscopy of a series of SiH4-treated calibration samples indicated that the surface pit and dislocation densities corresponded well up to a dislocation density of ~6 x 109/cm2. Above this point, surface-pit overlap meant that the dislocation densities determined by atomic force microscopy were underestimated. For all samples with dislocation densities below 6 x 109/cm2, spatial analysis of the surface-pit positions showed that the dislocations typically accumulated in bands at island coalescence boundaries.

Measuring Dislocation Densities in Nonpolar a-Plane GaN Films using Atomic Force Microscopy. M.A.Moram, C.F.Johnston, M.J.Kappers, C.J.Humphreys: Journal of Physics D, 2010, 43[5], 055303