Zero-phonon line associated with the midgap levelEL2in GaAs: Correlation with theAsGaantisite defect

The defect which brings about the zero-phonon line (ZPL) in the intracenter absorption spectra of the midgap level $\mathrm{EL}2\mathrm{}$ in GaAs (ZPL defect) is identified as the neutral charge state of the As antisite defect from the anticorrelative spectral dependency of the ZPL in optical absorption (OA) and the photo-EPR signal of ${\mathrm{As}}_{\mathrm{Ga}}^{+}$. This result gives definite evidence that $\mathrm{EL}2\mathrm{}$ and the As antisite are the same defect. The ZPL and its phonon replicas were also observed in the photocurrent (PC) spectra. The spectral dependency of the ZPL enhancement and quenching in PC exhibited an anticorrelative change with those in OA. The origin of this anticorrelative change was due to the contribution of carriers trapped in the shallow levels to PC.