It was recalled that hetero-epitaxial growth of AlxGa1–xN alloy films on GaN resulted in large tensile strain due to lattice mismatch. During growth, the strain was partially relieved by crack formation and the coupled introduction of dense misfit dislocation arrays. Extensive transmission electron microscopy measurements showed that the misfit dislocations entered the film by pyramidal glide of half-loops on the 1/3<1¯1▪3>/{11▪2} slip system: a well-known secondary slip system in hexagonal close-packed metals. Unlike the hexagonal close-packed case, where shuffle-type dislocations had to be invoked for this slip plane, it was shown that glide-type dislocations were also possible. Comparisons of measured and theoretical critical thicknesses showed that fully strained films could be grown into the metastable regime; which was attributed to limitations on defect nucleation. At advanced stages of relaxation, interfacial multiplication of dislocations dominated the strain relaxation process. This demonstrated that misfit dislocations were important mechanisms for the relaxation of strained III-nitride heterostructures that could contribute appreciably to the overall defect density.

Misfit Dislocation Formation in the AlGaN/GaN Hetero-Interface. J.A.Floro, D.M.Follstaedt, P.Provencio, S.J.Hearne, S.R.Lee: Journal of Applied Physics, 2004, 96[12], 7087-94