Phase separation and electronic structure of ZnS0.3O0.7 alloy thin film with and without (Ag, Li) co-doping

ZnS0.3O0.7 alloy thin film with and without Ag and Li co-doping are grown by pulsed laser deposition on c-plane sapphire substrate. The films are phase separated in S-rich and S-poor regions. Two and four different phases are observed to form in (Ag, Li)0.05:Zn0.95S0.3O0.7 and ZnS0.3O0.7 films respectively. Different phases and their relative volume fractions have been identified by electron diffraction pattern. The band gap corresponding to each phase is identified by low loss region of high resolution electron energy loss spectra. Band bowing parameter upon S doping is found to be 4.12 eV which closely match with Wien2k based density functional theory calculation utilizing mBJLDA exchange correlation potential. Oxygen positions have been replaced by sulphur in the lattice as confirmed by S L3,2 electron energy loss near edge absorption spectra. High resolution electron energy loss spectroscopy has been used to collect core level spectra of various dopants in order to identify their locations in the lattice. Experimental Ag M5,4 extended energy loss fine structure and Li K electron energy loss near edge structure in (Ag, Li):ZnS0.3O0.7 alloy have been compared with calculated spectra using FEFF code, suggesting that Ag and Li have taken up both the substitution and interstitial positions in the lattice. All the samples are resistive with resistance in the range of a few mega-ohms.