DEFECTS IN III-V MATERIALS AND THE ACCOMMODATION OF STRAIN IN LAYEREDSEMICONDUCTORS

High resolution monochromatic synchrotron-radiation diffraction images of five, high quality epitaxial heterojunctions on silicon, gallium a rsenide, and indium phosphide substrates display several forms of acco mmodation to lattice mismatch. From the images, we deduce a coherent s et of factors for the loss of crystalline order in layered semiconduct ing crystals. Lattice mismatch is demonstrated in each of the systems by warping after layer deposition. Nevertheless, local lattice orienta tion is maintained across each layer interface. In two of the systems, one severely mismatched while the other is not, no arrays of dislocat ions appear. Sets of mixed linear lattice mismatch dislocations, consi stent with identification as 60-degrees dislocations, are found in two of the other systems with intermediate degrees of mismatch. A set of pure edge dislocations penetrating all layers is found in a system wit h a grid structure. These observations indicate that the formation of extensive arrays of dislocations during uniform one micrometer layer d eposition depends not only on the extent of lattice mismatch and layer thickness but also on the degree of crystalline order of the substrat e. Establishment of a nonpseudomorphic layer mismatched with the subst rate by several tenths of a percent is an important factor, as previou sly determined. However, localized absence of crystalline order, e.g. in the form of scratches or dislocations in the substrate, appears als o to be required for the formation of arrays of interface mismatch dis locations. Where these criteria are not fulfilled, the formation of di slocations in uniform layered systems is inhibited. Localized residual stress can initiate dislocation formation even where it would not app ear in uniform layers. The images show also that crystalline disorder in state-of-the-art indium phosphide differs markedly from that in com parable gallium arsenide. Understanding of crystalline order in both m onolithic materials is extended by this work.