We investigated Pt island formation on surfaces of p-GaN (0001) epitaxial layer treated with HCl, annealed at 550 C for 10 minutes and nitrogen-sputtered for 15 minutes. Auger electron spectroscopy (AES), synchrotron photoemission spectroscopy (PES) and low energy electron diffraction (LEED) were used to study surface cleanliness, electronic properties and surface structure of the p-GaN (0001) surfaces, respectively. Using AES, Cl, C and N were found on the HCl-treated sample. After annealing at 550 C in vacuum for 10 minutes, Cl and C disappeared but oxygen was found instead. Sputtering of nitrogen ion onto the sample surface removed oxygen peak. Nitrogen was believed to replace oxygen in the surface layers of GaN crystal and results on a shift of Ga3d peak in PES results. LEED results taken at various electron beam energies demonstrated (1x1) surfaces. The closer the Ga 3d peak to the valence band edge indicates the smaller surface barrier height. After cleaning, platinum was e-beam evaporated on the clean p-type GaN (0001). One sample was studied as deposited and the other annealed at 530 °C for 1 minute in air. Atomic Force Microscopy (AFM) results show that after annealing at 530 °C for 1 minute in air, the number of islands increases. Cross-sectional Transmission Electron Microscopy (TEM) results show island thicknesses of ~4 nanometers. Lengths of the islands were found to vary from ~ 5-50 nm. High resolution electron micrographs (HREMs) suggest that islands formed on the non-damaged surface region. This indicate that cleaning process of the p-GaN wafer would result in difference microstructure and, hence, electronic properties of the contact between metal and p-GaN.

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