Plasmonic metal-to-semiconductor switching in Au nanorod-ZnO nanocomposite films.

We demonstrate conductivity switching from a metal to semiconductor using plasmonic excitation and charge injection in Au-nanorod (AuNRs)-ZnO nanocomposite films. ZnO films 12.6, 20.3, and 35.6 nm were deposited over AuNRs using atomic layer deposition. In dark conditions, the films transitioned from metallic to semiconducting behavior between 150 and 200 K. However, under sub-bandgap, white light illumination, all films behaved as semiconductors from 80 to 320 K. Photoresponse (light/dark conductivity) was strongly dependent on the thickness of ZnO, which was 94.4 for AuNR-12.6 nm ZnO and negligible for AuNR-35.6 nm ZnO. Conductivity switching and thickness dependence of photoresponse were attributed to plasmonically excited electrons injected from AuNRs into ZnO. Activation energies for conduction were extracted for these processes.