Realization of Ga-polarity GaN films in radio-frequency plasma-assisted molecular beam epitaxy

GaN heteroepitaxial growth on sapphire (0 0 0 1) substrates was carried out by radio-frequency (RF) plasma-assisted molecular beam epitaxy. The lattic e polarity of RF-MBE-grown GaN films on sapphire (0 0 0 1) substrates was i nvestigated as a function of buffer layer process. GaN films with Ga-face l attice polarity were fabricated using an AlN high-temperature buffer layer before GaN growth. Direct measurements by coaxial impact collision ion scat tering spectroscopy, as well as reflection high-energy electron diffraction , scanning electron microscope observations of surface morphologies and che mical etching, confirmed the polarity assignment. Realization of Ga-polarit y films on sapphire substrates by RF-MBE is a promising result and is expec ted to lead to a breakthrough in fabricating high-quality MBE-grown III-nit ride films for device applications. (C) 2000 Elsevier Science B.V. All righ ts reserved.