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 acceptors at equal rates, $1\pm 0.2{\mathrm{cm}}^{-1\mathrm{}}$. 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 $64\pm 10\mathrm{meV}$, 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.