Annealing effects of Au nanoparticles on the surface-plasmon enhanced p-Si/n-ZnO nanorods heterojunction photodetectors

Abstract

The effects of various annealing temperatures (350–550 °C) of Au nanoparticles (NPs) on the surface-plasmon enhanced p-Si/n-ZnO nanorods (NRs) heterojunction photodetectors (HPDs) have been investigated. The photoresponse of the surface-plasmon-mediated HPDs was found to be determined by the extinction band of the Au NPs, the defects of ZnO NRs, and the Schottky-barrier height (SBH) between the Au and ZnO interface. The higher annealing temperature (550 °C) causes more defects in ZnO NRs and lowers the ultraviolet (UV) response of the fabricated p-Si/n-ZnO NRs HPDs. The higher annealing temperature also renders a rougher surface in the Au NPs, thereby leading to destructive interference and hence the narrowest extinction band. In contrast, the modest temperature (450 °C) results in fewer defects in ZnO NRs, the widest extinction band in Au NPs, and the lowest SBH at the Au/ZnO interface. Such a result enhances the UV-to-visible rejection ratio from 439.6 to 6447 as compared to the HPDs without Au NPs. A band diagram considering the above investigations is illustrated to elucidate the surface plasmon resonance effects on enhancing the UV response.