High Resolution Optical Study of the Antisite Defect AsGa in GaAs; Correlation with Midgap Level EL2

A high resolution optical study was carried out on GaAs crystals containing only the EL2 midgap level. The no-phonon line at 1.039 eV was identified as an intracenter transition within AsGa. An excellent correlation was found between the intensity of the no-phot1n AsGa line and the characteristic EL2 absorption. A correlation was also found between the characteristic optical absorption of EL2 and its concentration as determined by DLTS measurements. These results prove the direct association of EL2 with a neutral state of AsGa The presence of another midgap level ELO, contained in heavily doped oxygen crystals had no effect on the optical spectra of EL2, but it did alter the DLTS measurements. Thus, an accurate calibration was obtained for the determination of EL2 by optical absorption based on DLTS measurements on crystals containing only EL2 and thus involving no uncertainties introduced by other midgap levels.