Direct evidence for the site of substitutional carbon impurity in GaAs

Abstract

Direct evidence that substitutional carbon in GaAs is predominantly on the As sublattice is obtained from Fourier transform infrared spectroscopy absorption measurements of the carbon-induced localized vibrational mode (LVM). The previously reported LVM absorption band of carbon is measured under high resolution conditions and is found to be the near superposition of at least four bands. It is shown by comparison with similar measurements of silicon-doped GaAs and by physical arguments that the only satisfactory explanation is that the bands arise from carbon on As sites with different nearest-neighbor configurations of the two Ga isotopes. There is no experimental indication of carbon on the Ga sublattice. These are the first observations of such shifts in LVM spectra for simple substitutional impurity defects in semiconductors.