Charge states and quantitative infrared spectroscopy of electrically active oxygen centers in gallium arsenide

Abstract

Oxygen-doped gallium arsenide crystals have been investigated by Fourier transform infrared spectroscopy. Samples with the Fermi level at about 0.4eV below the conduction band exhibit under thermal equilibrium conditions both stable states of electrically active oxygen Ooc, identified optically by the associated local vibrational modes at 730 and 715cm−1. Based on the analysis of compensating centers in the material and comparative Hall measurements, the charge states +1 and −1, respectively, are assigned to these bands. This result favors the (AsGa)2–OAs (two arsenic antisites and one off-center substitutional oxygen atom) microscopic model for the Ooc defect, presented recently, and is in disagreement with the earlier isolated OAs models. Systematic investigations related to the quantitative optical spectroscopy of this center using optically induced conversion experiments confirm that the absorption strengths of the two bands differ by 15%. A calibration factor of 3.6×1016cm−1 is suggested for the band at 730cm−1, derived indirectly from the variation of the +1 and −1 charge states with the carbon acceptor concentration.