Metastability of the Isolated Arsenic-Antisite Defect in GaAs

We propose that a neutral As-antisite defect in GaAs has a stable fourfold and a metastable, threefold interstitial configuration differing by 0.24 eV in their energies. The barrier height from the metastable to the normal state is calculated to be 0.34 eV. The metastable geometry is predicted to have a low optical excitation probability and to be electron-paramagnetic-resonance inactive. The two structural states of the antisite provide the simplest explanation for the unusual properties of the $\mathrm{EL}2\mathrm{}$ defect center in GaAs.