Stoichiometry-dependent vacancy formation in n-doped GaAs

The formation of vacancies in n-doped GaAs with variable stoichiometry was studied by means of positron annihilation. Highly Te-doped (n=1.5-5×10¹⁸ cm^-3) GaAs samples were annealed at high temperatures under variable arsenic vapor pressure (p_As) and rapidly quenched to room temperature. We found that monovacancies exist in Te-doped GaAs regardless of the annealing conditions. In contrast, the vacancy concentration was found to be dependent on p_As, i.e. on the stoichiometry. The vacancy concentration increases like p_As^1/4 and saturates at high As pressures (3-6 bar). This is a proof that the dominant vacancies in Te-doped As-rich GaAs are related to Ga vacancies, in agreement to theoretical results. Moreover, the vacancies were independently identified by using the Doppler broadening coincidence technique