Ambient dependent photoconductivity in Mg _x Zn_1−x O thin films

Mg _x Zn_1−x O (x = 0.0–0.08) thin films have been deposited on glass substrate by sol–gel technique and photoconductivity of the thin films have been investigated in vacuum, hydrogen, oxygen and air. Photoresponse spectra show that both ZnO and substituted films are ultraviolet light sensitive and the sensitivity shifts towards the shorter wavelength side with increasing x. The photo-to-dark current ratio (I _ph/I _d) and decay times are influenced by different ambient such as vacuum, hydrogen, and air for all the substituted films. I _ph/I _d for the substituted films increases first attaining a maximum value for x = 0.05 and then decreases for vacuum and hydrogen, while, an increase in the value is observed incase of oxygen as x increases. The change is not significant in air. The value of photo to dark current ratio for the films with x = 0.05 and 0.08 is as high as four orders of magnitude in both vacuum and hydrogen ambient. This change in the photo to dark current ratio is correlated with the grain boundaries, hence, the grain size of the films. In vacuum, hydrogen and oxygen, though a large increase in the photocurrent is caused, both growth and decay process becomes slower in these ambient.