Epitaxial layers were grown onto Si-terminated SiC or (00•1) sapphire substrates, and a detailed study of dislocations was carried out by means of Rutherford back-scattering channelling and X-ray diffraction. The annihilation of threading dislocations during growth was observed, by Rutherford back-scattering channelling, depending upon the type of substrate and the growth mechanism. The lowest dislocation densities were obtained for 2-dimensional growth on SiC substrates, and were of the order of 2 x 108/cm2. A reduction in the growth temperature from 1000 to 900C led to an increase in the dislocation density, by about an order of magnitude. For the first time in molecular beam epitaxially grown layers, during 2-dimensional growth, the formation of regularly shaped nanopipes within a screw dislocation was observed. The spirals were composed of monoatomic steps which surrounded nanopipes with diameters of 10 to 60nm.

Analysis of Dislocation Densities and Nanopipe Formation in MBE-Grown AlN-Layers D.G.Ebling, L.Kirste, M.Rattunde, J.Portmann, R.Brenn, K.W.Benz, K.Tillmann: Materials Science Forum, 2000, 338-342, 1549-52