Incorporation, diffusion, and electrical activity of Li in GaN

First-principles calculations are presented for Li, a group-I candidate acceptor, in GaN. Substitutional LiGa is a double acceptor with a low first ionization energy of 0.16 eV. Its straightforward use as p dopant is hindered by Li's concurrent preference for interstitialcy, which leads to self-compensation. Interstitial Li is predicted to diffuse freely in GaN above about 600 K, and to recombine exothermically with Ga vacancies producing LiGa, both results very closely matching recent experiments on implanted Li isotopes. The effects of this interstitial-substitutional transition on the doping state of GaN are discussed, with reference to the availability of Ga vacancies in chemical incorporation of implantation, and the role of Ga interstitial donors