ABSTRACTExposure to numerous acids and bases and UV/O3 oxidation were used to determine the best ex situ cleaning techniques for the (0001) surfaces of AIN and GaN. HF and HCI were the most effective in removing the oxide from AIN and GaN, respectively. However, AES and XPS revealed the surfaces to be terminated with F and CI which inhibited re-oxidation prior to loading into vacuum. TPD showed mat temperatures of 650 and 850°C are necessary to thermally desorb the CI and F, respectively. UV/O3 oxidation in air was not effective in removing hydrocarbons from either surface but was effective for oxide growth. In situ remote hydrogen plasma exposure at 450°C removed halogens and hydrocarbons remaining after ex situ cleaning of both AIN and GaN surfaces; however, oxide free surfaces could not be achieved. Thermal desorption of hydrocarbons from GaN in UHV was achieved at 650°C. Complete thermal desorption of the surface oxide in UHV was only achieved at temperatures > 800°C where some GaN decomposition occurred. Annealing GaN in NH3 at 700°C reduced the surface oxide without loss of surface stoichiometry.