Oxygen isoelectronic impurities in ZnTe: Photoluminescence and absorption spectroscopy

Oxygen substituting for Te in ZnTe is an isoelectronic impurity that traps excitons. The recombination radiation and absorption spectra attributed to isolated oxygen centers exhibit a no-phonon line accompanied by emission of multiple phonons. The two resulting spectra are ``mirror images'' of each other in energy with respect to that of the no-phonon line. Photoluminescence and absorption measurements on specimens with significantly higher oxygen concentration disclosed additional spectral features with four no-phonon lines, all displaced to lower energies with respect to that of isolated oxygen. Photoluminescence spectra of the present no-phonon lines show a temperature dependence characteristic of exchange coupling between an electron and a hole. Selective excitation with photon energies less than that of the no-phonon line of isolated oxygen permitted a clear observation of the features free from the phonon sidebands of isolated oxygen. These features, including phonon replicas, appear to be due to excitons bound to oxygen pairs, with different OO separations.