The structural and optical properties of rf magnetron-sputtered GaN thin films on p+-Si substrates have been accessed as a function of rapid thermal annealing (RTA) temperatures from 800 to 1000 °C. The evidence has revealed that higher RTA temperatures not only assist the GaN films in recrystallizing into stable hexagonal form but also enhance the near-band-edge emission of GaN films in the photoluminescence spectrum. Moreover, a deep electron trap (Et) with activation energy Ec-Et≅0.39 eV detected at the surface of higher-RTA-temperature-treated GaN films was asserted to be a nitrogen-vacancy-related defect that takes a defect-assisted-tunneling role in the forward conduction process of Au/GaN Schottky diode. The greater reverse leakage current and lower breakdown voltage are suggested to be due to the effects of a lower barrier height and higher ideality factor that occurred in the higher-RTA-temperature-treated samples. © 1999 American Vacuum Society.