Electronic and atomic structure of wide band gap GaN and thin aluminum adlayer studied with synchrotron radiation

Photoemission using synchrotron radiation has been used to study the electronic and atomic structures of the wide band gap semiconductor GaN surface and metal-GaN interfaces.; Angle resolved interband-transition measurements were made for normal emission as a function of photon energy and off-normal emission as a function of both photon energy and polar angle. Valence band dispersion along three major symmetry lines {dollar}GammaDelta{dollar}A, {dollar}GammaSigma{dollar}M and {dollar}GammaLambda{dollar}K of the Brillouin-zone were obtained and compared to the theory. Good agreement was found between the experimentally mapped valence bands and the calculated bands. An occupied surface state is found just below the valence band maximum which is independent of the perpendicular wave vector and also shows sensitivity to adsorbed species.; Atomic termination of the GaN surface is determined by ion scattering spectroscopy. The spectra clearly show a Ga-terminated surface. The local site symmetry for aluminum is determined from photon-energy-dependent photoelectron-diffraction data which are inverted by the holographic principle to obtain a real space image. This technique is a direct experimental measurement which is model independent. The transformed Al 2p emission data yield a real space image of the Al emitter's nearest neighbor atoms. The intensity of the transform shows that the Al has two in-equivalent adsorption sites. One is directly above the surface Ga, the on-top site, and the other involves replacing the surface Ga, the replacement site. The replacement site is found to be more favorable upon annealing.; High resolution core-level photoemmision with synchrotron radiation and LEED studies have been used to determine the growth morphology and electronic structures of the Al, Sb/GaN(0001) interface, and the interface upon annealing. The chemical reaction taking place at the Al sites on n{dollar}sp+{dollar}- and p-type GaN(0001) is followed using the photoemission spectra of the Ga 3d and Al 2p core-levels as a function of overlayer coverage, both at room temperature and upon annealing. The formation of a Schottky barrier is followed by accounting for the line-shape changes, the shifts of the bulk Ga 3d core-level binding energy, the change of surface work function, and the deduced dipole voltage contribution to the Schottky barrier height.