Influence of post-deposition annealing on structural, optical and transport properties of nanocomposite ZnO-Ag thin films

Thin films of ZnO and ZnO-Ag were grown by rf sputter deposition and post-annealed in air in the 300-600 °C temperature range. Annealing caused variation in strain in ZnO films and significant improvement of ZnO in ZnO-Ag films. The partial oxidation of Ag into AgxO upon annealing of ZnO-Ag films in air resulted in increase of transmittance, absorption due to AgxO phase, weakening of surface plasmon resonance absorption due to Ag nanocrystals and an increase in fluorescence. Surface studies indicate temperature induced particle transport cause agglomeration of nanocrystals in ZnO-Ag films during post-annealing. Annealed ZnO films showed a decrease in dark current and a sixteenfold increase in photocurrent at 3 V applied bias under white light illumination due to the formation of charged acceptors / oxygen vacancy centres, which was comparable to the white light photosensitivity of as-deposited ZnO-Ag film. For low applied bias voltages, Metal-Semiconductor-Metal photoconductive detectors made with annealed ZnO-Ag films showed potential for application as efficient deep ultraviolet (DUV) photodetectors with negligible sensitivity to white light and high sensitivity to DUV light.