EFFECT OF AS OVERPRESSURE ON SI-DOPED (111) A GAAS GROWN BY MOLECULAR-BEAM EPITAXY - A PHOTOLUMINESCENCE STUDY

We report on a photoluminescence investigation of heavily Si-doped (111)A-oriented GaAs samples. Molecular beam epitaxial growth has been performed with different As overpressures. The increase of the As pressure induces a site switching of Si from an As site (where Si is an acceptor) to a Ga site (where Si is a donor). This conversion from p- to n-type coincides with a change in the main point defect present in the sample: As vacancy (V(As)) for low As pressure and Ga vacancy (V(Ga)) for high As pressure. We suggest that their relative equilibrium is given by V(As) half arrow right over half arrow left V(Ga) + Ga(As) where Ga(As) is a gallium antisite, and that by increasing the As pressure this reaction is moved to the left.