In situ exposure of the. (0001) surface of AlN thin films to flowing ammonia at 1120 degreesC and 10(-4) Torr removes oxygen/hydroxide and hydrocarbon species below the detectable limits of x-ray photoelectron spectroscopy and decreases the Al/N ratio from 1.3 to 1.0. The positions of the Al 2p and the N 1s core level peaks acquired from the cleaned surfaces were 75.0 +/- 0.1 eV and 398.2 +/- 0.1 eV, respectively, which were similar to the values determined for the as-loaded samples. The cleaning process left unchanged the (1 X 1) low energy electron diffraction pattern, the step-and-terrace microstructure, and the root mean square roughness values observed for the surfaces of the as-loaded samples; i.e., the surface structure and microstructure were not changed by the high-temperature exposure to ammonia at low pressures. Vacuum annealing under 10(-7) Torr at 1175 degreesC for 15 min removed all detectable hydrocarbons; however, it did not remove the oxygen/hydroxide species. (C) 2005 American Vacuum Society.