Abstract
The oxidation of the GaN(0001) surface in the temperature range between 300 and 700 K has been studied by means of high-resolution electron energy loss spectroscopy (HREELS) and low-energy electron diffraction (LEED). The HREEL spectrum of the clean GaN surface exhibits a Fuchs–Kliewer (FK) mode at 702 cm −1, in good agreement with the calculated spectrum based on the dielectric theory. The band-gap of the clean GaN sample was determined to be 3.4±0.2 eV. After oxidation, a broad loss feature appeared on the high-energy side of the FK-mode of GaN. This loss structure shifted to higher energy with increasing adsorption temperature. The threshold for the band-gap transition also shifted to higher energy with increasing temperature of adsorption and annealing. These results indicate formation of islands of Ga-oxide and/or of Ga-oxinitride on the GaN surface. The LEED patterns before and after oxidation have a hexagonal structure which is characteristic for the wurtzite GaN film grown on a sapphire(0001).
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