Stoichiometry driven impurity configurations in compound semiconductors.
Precise stoichiometry and departures therefrom in the composition of the tetrahedrally coordinated compound semiconductors allow impurity incorporation in more than one configuration. Ultrahigh resolution infrared spectroscopy of CdTe:O at low temperatures reveals a unique sharp doublet associated with the local vibrational modes of OTe in a (OTe-VCd) complex with nearest neighbor Cd vacancy VCd and a single sharp line attributed to the local vibrational mode of OTe in a perfect CdTe. The uniaxial (C3v) symmetry of (OTe-VCd) transforms to Td symmetry at T* approximately 300 K, acquired due to an increasing rate of dynamic switching of the "OTe-VCd" dangling bond in which the vacancy and its three next nearest neighbor Cd cations exchange positions as temperature (T) approaches T*; for T>or=T*, the doublet thus transforms into a single, triply degenerate line.