Doping characteristics of O-implanted GaN have been investigated systematically from the viewpoint of annealing temperature. The implanted 0 atoms became electrically active as an n-type dopant after annealing above 1050degreesC, but with a low activation efficiency of only 1.1%. From variable temperature Hall effect measurements, O-implanted GaN displayed a shallow ionization level of similar to18.3 meV after 1100 and 1200 degreesC anneals. In addition, secondary ion mass spectrometry measurements showed no measurable redistribution of the 0 atoms by the annealing. These results indicate poor probability of the 0 atoms occupying an N lattice site in GaN. (C) 2003 American Vacuum Society.