BICRYSTALLOGRAPHY OF THE EPITAXIAL SYSTEMS III-V NITRIDES ON SAPPHIRE- THEORY AND EXPERIMENT

Orientation relationships (OR) for gallium, aluminium or indium nitrid es on sapphire substrates have been systematically studied, both theor etically and experimentally, as a function of substrate orientation. U sing an approach developed in this paper, all varieties of published O Rs have been classified into a few types. It is shown that the depende nce of ORs on both sapphire cut orientation and the layer compound can not be recognized within the framework of the commonly accepted coinci dence site lattices concept. Nevertheless, the dependence of ORs on th e layer compound for (0001) and (11 (2) over bar 0) sapphire substrate has been successfully described, without using any fitting parameters , by symmetry analysis as proposed previously by the authors and compu ter Monte Carlo simulation of the initial stage of epitaxy. The experi mental part of this paper consists of obtaining the nitride layers on sapphire substrate with various orientations and examining the ORs, ta king into account the direction of the polar sixfold axis, by both con ventional X-ray and Kossel line techniques. As a result, for the first time the ORs on all close-packed cuts of sapphire (with polarity) hav e been determined and a new type of OR for aluminium nitride has been found. All experimental data agree with theoretical considerations.