Enhanced band edge luminescence of ZnO nanorods after surface passivation with ZnS

We report on the passivation of surface defects of ZnO nanorods by surface layer deposition. ZnO nanorods and ZnSZnO hybrid nanostructures are grown on FTO coated glass substrate by chemical bath deposition method. XRD spectrum of ZnO nanorods shows the preferential growth along the c-axis. SEM analysis confirms the nearly aligned growth of the ZnO nanorods with a hexagonal shape. XPS measurements were performed to confirm the deposition of the surface layer and surface stoichiometry. Room temperature photoluminescence of ZnO nanorods showed two emission bands, viz. the band edge emission and the blue-green emission, with the latter being associated with the defect states arising from the surface of ZnO nanorods. The band edge emission is significantly increased as compared to blue-green emission after ZnS surface layer deposition on ZnO nanorods. The quenching of blue-green emission is explained in terms of reduced surface defects after ZnS deposition. Density functional theory (DFT) calculations are used to understand the mechanisms of defect passivation in ZnSZnO nanostructures and we show that the S atoms prefer the O site as compared with the Zn and interstitial sites.