Defect donor and acceptor in GaN

High-energy (0.7-1 MeV) electron irradiation in GaN grown on sapphire produces shallow donors and deep or shallow accepters at equal rates, 1 +/- 0.2 cm(-1). The data, in conjunction with theory, are consistent only with the shallow donor being the N vacancy, and the acceptor the N interstitial. The N-vacancy donor energy is 64 +/- 10 meV, much larger than the value of 18 meV found for the residual donor (probably Si) in this material. The Hall-effect measurements also reveal a degenerate n-type layer at the GaN/sapphire interface which must be accounted for to get the proper donor activation energy.