Resolved structure in the quenching band of the EL2 center in GaAs, studied by infrared spectroscopy

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Abstract
Infrared measurements at low temperature on undoped semi-insulating GaAs reveal additional details in the photoresponse of the EL2 center. In the continuous spectral recording of the optical cross section for the bleaching of the EL2 absorption the zero phonon line (ZPL) at 1.039 eV and six phonon replicas with 11 meV separation have been observed. A modified Huang Rhys calculation is necessary to reproduce both the relative intensity of the ZPL and the maximum of the broad band at 1.17 eV. Using the intensity of the resolved structure for calibration, we calculate the contribution of the intracenter transition to the total EL2 absorption spectrum. Comparison with the known time constants for photoionization and quenching yields a probability of (1.2±0.3)% for transformation to the metastable state after intracenter excitation. The ZPL in the absorption spectrum shows considerable broadening and a decrease in energy by 3 meV in the temperature range 10–65 K.