Symmetry of theEL2defect in GaAs

From experiments on the stress-induced splitting of the zero-phonon line associated with the optical-absorption band originating from photoexcitation of the EL2 center in GaAs, Kaminska et al. concluded that this center has tetrahedral symmetry, which would account for its simple point-defect structure. An alternative explanation of the observed splitting pattern, which involves an orthorhombic center of $C_{2v}$ symmetry, is discussed in this paper. This would account for both the recently revealed complex structure of EL2 and its apparent high symmetry.