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 $\mathrm{CdTe}:\mathrm{O}$ at low temperatures reveals a unique sharp doublet associated with the local vibrational modes of ${\mathrm{O}}_{\mathrm{Te}}$ in a (${\mathrm{O}}_{\mathrm{Te}}\mathrm{\text{−}}{V}_{\mathrm{Cd}}$) complex with nearest neighbor Cd vacancy $V_{\mathrm{Cd}}$ and a single sharp line attributed to the local vibrational mode of ${\mathrm{O}}_{\mathrm{Te}}$ in a perfect CdTe. The uniaxial (${\mathrm{C}}_{3v}$) symmetry of (${\mathrm{O}}_{\mathrm{Te}}\mathrm{\text{−}}{V}_{\mathrm{Cd}}$) transforms to $T_d$ symmetry at $T^{*}\sim 300\mathrm{K}$, acquired due to an increasing rate of dynamic switching of the “${\mathrm{O}}_{\mathrm{Te}}\mathrm{\text{−}}{V}_{\mathrm{Cd}}$” dangling bond in which the vacancy and its three next nearest neighbor Cd cations exchange positions as temperature ($T$) approaches $T^{*}$; for $T\ge T^{*}$, the doublet thus transforms into a single, triply degenerate line.

• Received 26 October 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.035508