Cathodoluminescence of GaN films grown under Ga and N rich conditions by radio-frequency-molecular beam epitaxy

Cathodoluminescence (CL) topographs were taken at room temperature at 364 nm on undoped GaN films grown by plasma-enhanced molecular beam epitaxy at various V/III ratios. The CL topographs were compared with scanning electron microscope (SEM) images. The CL topograph was found to be significantly influenced by the V/III ratio during growth. For GaN films grown at low V/III ratio, spatially nonuniform luminescence intensity was observed. This nonuniformity in luminescence may be due to the local variation of stoichiometry of GaN induced by Ga microsegregation. At nitrogen-rich condition, almost flat surfaces in SEM image were observed and the uniform intensity of luminescence was obtained by CL topograph. Thus, the nitrogen-rich condition is favourable to get structually and optically uniform films.