Anharmonicity of the C-As local oscillator in gallium arsenide

The local vibrational modes of the anion-site substitutional defect C-As have been investigated by Fourier transform absorption spectroscopy in the temperature range between 10 and 450 K. A new, thermally activated line at 576.5 cm(-1) (300 K) is attributed to the Gamma(5)(v=1) --> Gamma(5)(v=2) transition. The analysis in terms of an anharmonic oscillator of T-d symmetry gives the cubic potential parameter \B\ = 6.4x10(12) J/m(3). The fine structure of the second harmonic transition Gamma(1)(v=0) --> Gamma(5)(v=2) due to host isotope effects has been detected at low temperatures. Results of calculations using a harmonic perturbation theory are presented.