Photoresistance of Li$_{0.2}$Zn$_{0.8}$O thin films and Li$_{0.2}$Zn$_{0.8}$O/Al$_{0.15}$Zn$_{0.85}$O multilayers

Thin films of Li$_{0.2}$Zn$_{0.8}$O and Li$_{0.2}$Zn$_{0.8}$O/Al$_{0.15}$Zn$_{0.85}$O multilayers have been grown on sapphire substrates by pulsed-laser deposition. P-type Li$_{0.2}$Zn$_{0.8}$O is an insulator with the band gap of 3.26eV and n-type Al$_{0.15}$Zn$_{0.85}$O is a transparent conductor. Under the ultraviolet light irradiation, the Li$_{0.2}$Zn$_{0.8}$O films show photoresistance (PR) (PR=(R$_{dark}-$R$_{irradiation})$/R$_{irradiation})$ effect of $\sim $340{\%} at room temperature. In bilayers of Li$_{0.2}$Zn$_{0.8}$O($\sim $110nm)/Al$_{0.15}$Zn$_{0.85}$O($\sim $90nm) where a p-n junction is formed, the photoresistance increases to $\sim $8600{\%}. The photoresistance dependence on wavelength (300-700nm) measurement shows that the photoresistance effect is observed when the light wavelength is below $\sim $380nm. The dependence of the light intensity and the response time of the resistance switching have also been measured and will be discussed. The largely enhanced PR effect in bilayers is probably due to the enhancement of the PR effect in p-n junctions. The increased photosensitivity indicates that the Li$_{0.2}$Zn$_{0.8}$O/Al$_{0.15}$Zn$_{0.85}$O multilayers are promising for UV photodetection applications.