Experimental results of photoexcitation and thermal deactivation of localized vibrational mode absorption of the oxygen-vacancy complex in GaAs are reported. Two levels within the energy gap are observed, one located at 0.14 eV and the other between 0.57 eV and 0.75 eV below the conduction-band minimum. It is proposed that this center exhibits a negative U property with the second electron ionization energy higher than that of the first electron.
Experimental results of deep level transient spectroscopy (DLTS) and Fourier transform infrared spectroscopy (FTIR) on oxygen-doped GaAs crystals are presented. A positive identification of the DLTS signature of the Ga-O-Ga defect (tentatively identified as an oxygen-arsenic vacancy complex) is made through correlation with FTIR measurements. The energy level for the two-electron state of the defect is found to be located at 0.55 eV below the conduction band, and direct proof is given that this center is actually a negative U center. A calibration factor for local vibrational mode absorption is calculated to be 8×1016 cm−1.
A series of isochronal annealing experiments have been performed on bulk GaAs crystals doped with oxygen. Two centers induced by oxygen, the isolated oxygen interstitial (Oi) and the gallium-oxygen-gallium (Ga-O-Ga) defect, most likely due to oxygen interstitial-arsenic vacancy complex, were monitored using localized vibrational mode absorption. The Ga-O-Ga center dissociates at temperatures above 650 °C resulting in an increase of the Oi concentration. Using the known oscillator strength of Ga-O-Ga transition, the calibration factor between integrated absorption and concentration of isolated oxygen interstitial was determined to be 8×1016 cm−1. The observed increase of absorption bands of both defects after high-temperature annealing indicates that other types of oxygen-containing defects are present.
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