GaN thin films were grown by molecular beam epitaxy on sapphire substrates. 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. Cathodoluminescence (CL) spectra of the films feature bright UV exciton peaks and a broad green emission band. We identify the exciton peaks as those of the wurtzite form of GaN. A comparison of SE and CL micrographs of the same sample area shows that the luminescence emanates almost entirely from the hexagonal crystallites.
- GaN films
- sapphire substrates