MORPHOLOGY OF LUMINESCENT GAN FILMS GROWN BY MOLECULAR-BEAM EPITAXY

GaN thin films were grown by molecular beam epitaxy on sapphire substr ates. Scanning electron (SE) and atomic force microscopies reveal that on a typical film an assembly of oriented hexagonal microcrystallites rises above a background of polycrystalline or amorphous material. Ca thodoluminescence (CL) spectra of the films feature bright UV exciton peaks and a broad green emission band. We identify the exciton peaks a s those of the wurtzite form of GaN. A comparison of SE and CL microgr aphs of the same sample area shows that the luminescence emanates almo st entirely from the hexagonal crystallites. (C) 1996 American Institu te of Physics.