The EL2 center in GaAs: symmetry and metastability

(Received 22 May 1991, accepted I2 June 1991)

Abstract
Photo-EPR, piezospectroscopic and Stark-effect photocapacitance data were used to determine the symmetry of the EL2 center in GaAs and to identify the mechanism that underlies its metastable behavior. The results unambiguously point to C as the type of symmetry for this antisite double donor whose charge states - D ⁺ = As _Ga, D ⁰= (As V ) ⁰ and D ⁺⁺ = (As V ) ⁺⁺ - occupying, respectively, the positions on the site and in the tetrahedral and hexagonal interstices, are brought about, in the same order, by the wavefunctions of the , L and X valleys of the conduction band. The transition made by the EL2 center to a metastable state is the result of a charge exchange of the type 2D ⁺ + D ⁰ + D ⁺⁺ , which causes the antisite As, defect to tunnel from its position at the site to a position in the tetrahedral interstice. Annealing of the center in this state proceeds at such temperatures and rates as are determined by the height of the energy barrier to the D ⁰ + D ⁺ reaction.