Composition dependent ultraviolet photoresponse in MgxZn1−xO thin films

Mg x Zn 1 − x O (0.0⩽x⩽0.12) thin films have been deposited on glass substrates by sol-gel process. The hexagonal wurtzite structure of ZnO is retained in the Mg-substituted films. From the photoresponse measurements, it is observed that both ZnO and substituted films are UV sensitive and with increasing Mg content, the sensitivity shifts toward the shorter wavelength side with a gradual decrease in magnitude. The UV-to-visible current ratio remains almost constant up to x=0.08 and thereafter decreases. The decay time for 90% photocurrent gradually decreases to less than 4s for x=0.05 followed by an increase for higher values of x. The decay time is faster than the growth time for all the substituted films. The change in the photoconductivity with Mg content (x) is correlated to the microstructural change. A trap level, found to be involved in the photoconductivity, is located at ∼0.8eV below the conduction band. The photo-to-dark current ratio (Iph∕Id) gradually decreases from three orders of magnitude to one order with the increase in the Mg content.