Self-Nucleated Thin Films of GaN and Al x Ga1−x N for Optoelectronic Devices: Structure and Morphology

Abstract There is increasing interest in the use of Group IIIA nitrides (A1N, GaN, InN, and their alloys) for a variety of optoelectronic applications, including short wavelength sources and detectors. Progress, while spectacular these past few years, has been hampered by the lack of bulk, lattice-matched material to serve as the substrate for homoepitaxial growth. The most common substrate, basal plane sapphire, with a 16% lattice mismatch, requires a predeposited nucleation layer to achieve pseudo two-dimensional layer-by-layer growth suitable for device processing. The surface morphology and mosaic dispersion of both unnucleated and self-nucleated GaN thin films have been studied by a combination of real space images from atomic force and scanning tunneling microscopies and reciprocal space intensity data from X-ray scattering measurements. The unnucleated GaN films show a large-grained hexagonal relief, typical of three-dimensional island growth, while the self-nucleated films are shown to be dense mo...