Photoconductivity properties of silver-doped zinc oxide films

The transient photoconductivity of as-deposited and annealed in air 0.27 at.% silver-doped zinc oxide films (Ag:ZnO) coated on sapphire substrates by e-beam evaporation method was measured in the dark (σd) and under light from a solar simulator (σph) at temperatures 8, 12, and 32 °C. In comparison with as-deposited Ag:ZnO film, the annealed film exhibits lower photoresponse which decreases and becomes slower as the temperature increases from 8 to 32 °C. The ln σd versus 1/T plots of the as-deposited and annealed samples revealed thermally-activated process in the range of 5–60 °C for σd with an activation energy of 1.4 eV and 0.8 eV, respectively. Furthermore, σd and σph were measured in the frequency range of 10–35 × 106 s−1 at room temperature. σd of the as-deposited film is frequency independent, while σd of the annealed film exhibits two different conduction mechanisms; one dominates in the low-frequency region as conduction via delocalized states, and the other is the polaron mechanism, which is activated at higher frequencies (ω > 190 × 103 s−1). The frequency dependences of σph of the as-deposited and annealed films obey the Drude model of conductivity.