The dislocations of low-angle grain boundaries in GaN epilayers: a HRTEM quantitative study and finite element stress state calculation

During epitaxy of GaN on sapphire grains form a mosaic structure. The distance between edge dislocations in these boundaries is from 2 to 15 nm. The strain around the dislocations is quantitatively measured by processing of HRTEM images. The dislocation core distribution maps and in plane Burgers vectors components are derived from the experimental strain tensor by applying the continuum dislocation theory. Experimental results were compared with the atomic models of edge dislocations calculated using a modified Stillinger-Weber potential for different atomic configurations of the cores. It is concluded that the strain field extracted from simulated images matches with that of observed dislocations. Starting from experimental distortion distribution data, the finite element calculations are used to estimate the stress around the boundaries. (C) 2002 Elsevier Science B.V. All rights reserved.