Temperature dependence of very deep emission from an exciton bound to an isoelectronic defect in polycrystalline CulnS_2

摘要

Zero-phonon lines (ZPLs) of deep exciton bound to isoelectronic deep-donor-deep-acceptor pair in CuInS_2 are studied by photoluminescence. These ZPLs have peak positions at 0.6241 eV (A line) and 0.6220 eV (B line), followed by two series of phonon replicas with phonon energies of 8 and 40.5 meV. Temperature dependence of the intensity of these ZPLs is explained by electron-phonon coupling to a single phonon mode with energy of 8 meV and shows that the lines are originated from two excited state levels of the same exciton. The (anomalously strong) temperature broadening of ZPLs follows ～T~(2.6) law and can be explained by assuming a strong vibronic coupling between two excited states.