The formation of mismatch dislocations in layered semiconductor structures was found recently in high resolution monochromatic synchrotron x-radiation diffraction images to be correlated with characteristics of the substrate as well as with the layer thickness and degree of lattice mismatch of non pseudomorphic layers.1,2 We have now extended these studies to examine the accommodation to strain as a function of lattice mismatch in a series of high electron mobility transistor (HEMT) structures grown by molecular beam epitaxy (MBE) on indium phosphide substrates.
Five distinct types of irregularity are observed: 1) lattice warping, 2) the formation of a nonpseudomorphic layer, 3) the formation of extended arrays of linear mismatch dislocations at the interface between the substrate and a nonpseudomorphic layer, 4) the formation of oval regions of tweed-like local lattice variation imbedded among these arrays, and 5) extended tweed-like local lattice variation over large peripheral areas in which the formation of straight mismatch dislocation arrays is not observed.
Warping of the lattice is found in nearly all layered structures. A distinct layer with a different lattice parameter but without visible misfit dislocations is formed with a mismatch of 0.27 %. With increase of the mismatch to 0.5 %, the other three forms of accommodation appear in distinct regions of the structure: arrays of <011> mismatch dislocations; oval regions of tweed-like irregularity, oriented in the  direction; and peripheral regions of extended tweed-like local lattice variation.
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