Origin of a Localized Vibrational Mode in a GaSb Substrate With a MBE-grown ZnTe Epilayer*

In the infrared spectrum of a MBE-grown ZnTe epilayer grown on GaSb, a localized vibrational mode (LVM) is observed with a remarkable fine structure. On the basis of the Zn and Te deposited on the GaSb substrate during the MBE growth of ZnTe, it is deduced that $^{64}$Zn, replacing Sb substitutionally as an anti-site impurity, is responsible for the LVM. The fine structure can then be interpreted in terms of the infrared active modes of a XY$_{4}$ quasimolecule, X$\equiv$$^{64}$Zn and Y$\equiv$$^{69}$Ga and $^{71}$Ga occupying the nearest neighbor sites, reflecting all the possible combinations and permutations as well as their natural isotopic abundance.