PLASMA CLEANING AND NITRIDATION OF SAPPHIRE SUBSTRATES FOR ALXGA1-XN EPITAXY AS STUDIED BY X-RAY PHOTOELECTRON DIFFRACTION

The influence of plasma and thermal treatments on the structure and co mposition of sapphire (00.1) surfaces has been studied by hemispherica lly recorded x-ray photoelectron spectroscopy and diffraction (XPD) to better understand the surface conditioning during the growth initiati on procedure for the epitaxy of GaN: A treatment involving an O-2 plas ma generated by electron cyclotron resonance is shown to efficiently r emove surface contamination and to produce well-ordered surfaces. Afte r a thermal treatment in vacuum the sapphire (00.1) surface becomes te rminated by Al atoms. ALN films with good short-range order are obtain ed by a simple high temperature nitridation step in the metal organic chemical vapor deposition reactor. A novel direct crystallographic met hod termed CHRISDA is employed for the analysis of the XPD data. By an alysis of the XPD patterns the crystal structure of sapphire is found to extend into the probed near surface region without significant pert urbations. The ALN layers formed by thermal nitridation were found to crystallize in the hexagonal phase and to be terminated by nitrogen at oms. (C) 1998 American Vacuum Society. [S0734-2101(98)04104-9].