Improved deep ultraviolet light photosensitivity of nanocomposite ZnO–Ag films deposited with substrate heating

Abstract

The structural and photosensing properties of nanocomposite ZnO–Ag films deposited with substrate heating at 300 °C and subsequent post-annealing upto 600 °C are reported. Nanocomposite ZnO–Ag thin films deposited at a substrate temperature of 300 °C and post-annealed in air at 425 °C showed a red shift of surface plasmon resonance peak upto 114 nm. This result is explained using electron transfer mechanism from Ag nanocrystals (NCs) to ZnO NCs and it is inferred that AgO phase was not formed at the interface of ZnO and Ag NCs. These films showed lower dark current values, negligible white light photosensitivity (∼1.35–1.04) and higher photosensitivity (∼5.0 × 103 at 1 V) to deep ultraviolet light (DUV) and demonstrated thermal stability upto 425 °C. However, ZnO–Ag films post annealed at 500 °C–600 °C showed increase of intensity of (100) and (101) planes of ZnO, oxidation of Ag nanocrystals (NCs) and an increment in white light sensitivity (∼1.65 to 2.84) at 1.0 V applied bias. These results are explained using band diagram for ZnO/Ag–NC/AgO phases. Further, films deposited with 600 °C substrate temperature showed higher dark current and photocurrent values. Hot electrons photoexcited in ZnO NCs (with Eg: ∼3.24 eV) upon illumination with DUV light (photon energy range: 4.43–5.63 eV), and the energetic electrons transferred from Ag–NCs into ZnO conduction band in the as-deposited and 425 °C annealed films, contributed to the high photosensitivity at low applied bias of 1.0 V.