ANTISITE-INTERSTITIAL-COMPLEX MODEL FOR THE EL2 DEFECT IN GAAS

The suitability of an As-derived antisite-intersitital-complex model for the EL2 defect center in semi-insulating GaAs is examined via first-principles pseudopotential calculations. The structure most consistent with electron-nuclear-double-resonance data consists of a positively charged As antisite (A) bound to a negatively charged twofold-coordinated As interstitial (I). Depending on its precise structure, the A-I axis deviates by 10-degrees-14-degrees from the (111) cubic axis and the A-I separation varies from 6.3 to 5.1 angstrom. The maximal bond-angle variation around the antisite is 2-degrees-8-degrees from the ideal tetrahedral value for these structures. A major problem with the distant-pair antisite-interstitial model for EL2 is that it is unstable with respect to atomic rearrangement leading to a nearest-neighbor split-interstitial bonded configuration. The consistency of the model with other experimental data is examined.