Electron paramagnetic resonance (EPR) spectroscopy is used to study the unpassivated Mg-related acceptor in GaN films. As expected, the trends observed before and after O2, N2, or forming-gas anneals at temperatures <800°C are similar to those typically reported for electrical measurements. However, annealing at temperatures >850°C in O2 or N2 permanently removes the signal, contrary to the results of conductivity measurements. Approximately 1019 cm -3 Mg acceptors were detected in some GaN films grown by chemical vapor deposition (CVD) before acceptor activation, suggesting that it is possible to have electrically active Mg in as-grown CVD material.
