Heteroepitaxy of gallium nitride layers: The role of initial stages in film formation

Epitaxial gallium nitride films are important structural components in devices of short-wavelength electronics. Presently, absence of a perfect substrate material is a considerable restraint on the development of devices based on gallium nitride. The process of nucleation and subsequent evolution of GaN on the substrate surface covered with a buffer layer was investigated theoretically. The rates of nuclei flows and the size distribution functions for the islands formed at substrate temperatures T > 480 deg C were calculated for substrates covered with AIN buffer layers. All the major mechanisms of island growth were considered. It has been shown that at a temperature of T = 480 deg C islands of liquid Ga are first formed. Next, chemical reactions between gallium and nitrogen with formation of GaN take place on the substrate surface. At 750 deg C > T # > deg C, only GaN is nucleated. The Ostwald ripening process in an ensemble of GaN islands was studied and a phase diagram of such an ensemble constructed.