X-ray diffraction peak profiles from threading dislocations in GaN epitaxial films

We analyze the line shape of x-ray diffraction profiles of GaN epitaxial layers with large densities of randomly distributed threading dislocations. The peaks are Gaussian only in the central, most intense part of the peak, while the tails obey a power law. The q(-3) decay typical for random dislocations is observed in the rocking curves with open detector. The entire profile is well fitted by a restricted random dislocation distribution. The densities of both edge and screw threading dislocations and the ranges of dislocation correlations are obtained.