Photo-induced electronic transition and effect of thickness on the resistivity of Li-doped ZnO thin films

Abstract

Zn1−xLixO (x = 0, 0.005, 0.010 and 0.015) thin films were grown on single-crystal sapphire (Al2O3) substrates (001) by pulsed laser deposition method. We prepared two sets of thin films. In set-1, the doping of Li was varied. A fractional Li-doping causes a systematic rise in the temperature-dependent resistivity of the films. Further, the ultraviolet (UV) light (365 nm) exposure on these films causes a variety of effects. We observed a UV light-induced metal-semiconductor transition in otherwise semiconducting films. The transition manifests in a temperature range above 200 K to 300 K. In set-2, thin films of maximum doping (1.5%) were prepared by varying the thickness. The structural study revealed that the films are crystalline and oriented towards c-axis of wurtzite ZnO. The temperature-dependent resistivity measurements show the increase in resistivity with an increase in the thickness of the films.