Regions of p-type material were produced in undoped GaN films by Be+ and Be++O+ implantation and subsequent annealing between 1000 and 1050C. From thermal admittance spectroscopic measurements, the activation energy of the Be acceptor level was found to decrease from ~0.240 to ~0.163eV by the implantation of additional O atoms, which was in reasonable agreement with the improvement in p-type doping characteristics determined by room-temperature Hall-effect measurements. These results indicated that Be++O+ co-implantation reduced the depth of the Be acceptor level based upon a site-competition effect. Therefore, these acceptor levels were most probably due to Be atoms at interstitial and Ga-lattice sites.

Effect of Be++O+ Co-Implantation on Be Acceptors in GaN. Y.Nakano, T.Kachi, T.Jimbo: Applied Physics Letters, 2003, 82[13], 2082-4