Bicrystallography of the Epitaxic Systems `III-V Nitrides on Sapphire': Theory and Experiment

Orientation relationships (OR) for gallium, aluminium or indium nitrides on sapphire substrates have been systematically studied, both theoretically and experimentally, as a function of substrate orientation. Using an approach developed in this paper, all varieties of published ORs have been classified into a few types. It is shown that the dependence of ORs on both sapphire cut orientation and the layer compound cannot be recognized within the framework of the commonly accepted coincidence site lattices concept. Nevertheless, the dependence of ORs on the layer compound for (0001) and (110) sapphire substrate has been successfully described, without using any fitting parameters, by symmetry analysis as proposed previously by the authors and computer Monte Carlo simulation of the initial stage of epitaxy. The experimental part of this paper consists of obtaining the nitride layers on sapphire substrate with various orientations and examining the ORs, taking into account the direction of the polar sixfold axis, by both conventional X-ray and Kossel line techniques. As a result, for the first time the ORs on all close-packed cuts of sapphire (with polarity) have been determined and a new type of OR for aluminium nitride has been found. All experimental data agree with theoretical considerations.