Optical Properties of As-Antisite andEL2Defects in GaAs

This Letter reports the first application of an ESR-tagged magnetic circular dichroism measurement to a paramagnetic deep-level defect in a semiconductor. In semi-insulating GaAs two new absorption bands are found at 1.05 and 1.29 eV. Both bands are identified as intracenter electronic transitions of the As-antisite defect. The analysis of the absorption and concentration data implies that the "dominant electron trap" ($\mathrm{EL}2$) in GaAs is not the As antisite.