A grid of regularly-distributed misfit dislocation arrays was observed in GaN films

grown on AlN buffer layers by plan-view and cross-sectional transmission electron

microscopy. It was found that the spacing of the misfit dislocation arrays decreased

with increasing GaN film thickness. Before the formation of grids in very thin GaN

films, short misfit dislocations originated around and bordered on long dislocations

probably in order to achieve an isotropic strain relaxation, which indicate that the

misfit dislocation grid was formed by a progressive introduction of misfit

dislocations with the GaN growth. Furthermore, high-resolution transmission

electron microscopy displays that, due to large misfit strain between GaN and AlN,

a part of the misfit dislocations was produced by interfacial migration of preexisting

threading dislocations in AlN layers at the early stage of the GaN growth.

The misfit dislocations in GaN were thus proposed to be introduced first by

interfacial migration of threading dislocations in AlN and then gradually form into

a grid around the misfit segments of threading dislocations. This was supported by

a good agreement between experimental stain values of the GaN films and a

theoretical prediction based on the threading dislocation migration.

Generation of Misfit Dislocations in Highly Mismatched GaN/AlN Layers. J.Bai,

T.Wang, K.B.Lee, P.J.Parbrook, Q.Wang, A.G.Cullis: Surface Science, 2008,

602[15], 2643-6