The Gibbs free energy of formation (formation enthalpy and entropy), as well as the charge state of Ga vacancies in n-type GaAs, were determined by directly probing the vacancy concentration as a function of annealing temperature, As vapor pressure and doping concentration using positron annihilation. The Ga vacancy concentration increased with dopant concentration and As vapor pressure, but decreased with temperature. Using equilibrium thermodynamics, a -3e charge state of the Ga vacancy in n-doped GaAs was obtained, as well as a formation enthalpy of 3.2eV and a formation entropy of 9.6k for the uncharged vacancy state.

Determination of the Gibbs Free Energy of Formation of Ga Vacancies in GaAs by Positron Annihilation. J.Gebauer, M.Lausmann, F.Redmann, R.Krause-Rehberg, H.S.Leipner, E.R.Weber, P.Ebert: Physical Review B, 2003, 67[23], 235207