SELF-NUCLEATED THIN-FILMS OF GAN AND ALXGA1-XN FOR OPTOELECTRONIC DEVICES - STRUCTURE AND MORPHOLOGY

There is increasing interest in the use of Group IIIA nitrides (AIN, G aN, InN, and their alloys) for a variety of optoelectronic application s, including short wavelength sources and detectors. Progress, while s pectacular 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% l attice mismatch, requires a predeposited nucleation layer to achieve p seudo two-dimensional layer-by-layer growth suitable for device proces sing. 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 microsco pies and reciprocal space intensity data from X-ray scattering measure ments. 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 mosaics of highly oriented islands emblem atic of a more two-dimensional growth. High quality AlxGa1-x alloy fil ms have also been deposited on self-nucleated sapphire substrates and exhibit minimal homogeneous and inhomogeneous strain and alloy cluster ing. Consistent with their reduced strain and chemical uniformity, the se wide-bandgap AlxGa1-xN films are suitable for a number of optoelect ronic applications.