Ab initio calculations on the defect structure of β-Ga2O3

The intrinsic point defects of beta-Ga2O3 are investigated using density functional theory. We have chosen two different exchange-correlation potentials: the generalized gradient approximation (GGA) and a hybrid potential (HSE06). Defect formation energies were determined taking into account finite-size effects. Schottky, anti-Frenkel, and Frenkel energies have been extracted for T = 0 K. We calculate formation entropies for an oxygen and a gallium vacancy and determine the Gibbs energy of Schottky disorder. Furthermore, we investigate the defect concentrations as a function of the oxygen partial pressure. The obtained purely intrinsic defect concentrations for charged defects are very small and result in a pO(2) dependence of the electron concentration of [e'] similar to pO(2)(-1/6), whereas experimentally [e'] similar to pO(2)(-1/4) is found. So we assume that, experimentally, a small unintentional donor doping is unavoidable. A small extrinsic donor concentration [D-.] = 10(18) cm(-3) (10 ppm) changes the electron concentration to [e'] similar to pO(2)(-1/4) and gives an activation energy of the conductivity sigma of 1.7 eV in good agreement to experimental values. So we propose as majority disorder 3[V'''(Ga)] = [D-.] with electrons being minority defects.