We propose that $\mathrm{DX}$ is a negatively charged defect center resulting from the "reaction" $2d^0\to d^{+}+D{X}^{-}$ where $d$ represents a substitutional donor. The results of our pseudopotential calculations for Si- and S-induced $\mathrm{DX}$ centers in GaAs indicate large dopant-dependent relaxations leading to threefold-coordinated interstitial sites for either the donor or one of its nearest neighbors. A simple expression for the alloy composition and pressure dependence of the $\mathrm{DX}$ binding energy is suggested and used in an analysis of experimental data.

• Received 24 May 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.873