Photoconducting and Photoresponse Studies on Multilayered Thin Films of Aluminium Doped Zinc Oxide

Aluminium doped zinc oxide (Zn_1-xAl_xO) thin films were deposited by sol-gel spin coating technique onto a glass substrate (x=0-5wt%). The films were characterized by UV-Visible spectroscopy, SEM and were subjected to photoconductivity, temperature dependant conductivity and photo response measurements. The film with Al-1.5wt% showed the maximum absorption in UV and had a good optical transmission (~75%) in the visible regions respectively. The SEM images showed crack free films with little grain boundaries with decrease in grain size at higher aluminium concentration. The photoconductivity measurements reveal that there is a phenomenal increase in the photocurrent upon doping compared to undoped ZnO. The photocurrent reaches its maximum value (25μA) at 10V which is nearly 50 times more than the dark current (0.44μA) for Al-1.5wt% doped ZnO. The photocurrent then decreases for further increase in Al concentration. The photoresponse study gives the measure of rise and decay time. The rise time was found to be shorter for Al-1.5wt% among the doped film but longer than undoped ZnO. The temperature dependant conductivity shows that the thermal activation energy for the film decreases at Al-1.5wt% aluminium concentration and then increases for other concentrations in the temperature range 300-400K. The optimum conditions for maximum photoconductivity and photoresponse have been studied for photoconductive applications and the results presented.