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/spl times/10/sup 18/ cm/sup -3/) GaAs samples were annealed at high temperatures under variable arsenic vapor pressure (p/sub 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/sub As/, i.e. on the stoichiometry. The vacancy concentration increases like p/sub As//sup 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.