Instability of UV Photoresponse in MgZnO Thin Films and Its Improvement by MgO Capping

Herein, it is shown that the UV photoresponse characteristics of MgZnO thin films deposited by pulsed laser deposition change rapidly with time if the films are exposed to ambient air and that the response can be stabilized significantly by depositing a thin capping layer of MgO on the surface of MgZnO thin film. The decay time of photocurrent in as-deposited MgZnO thin films increases from 1.8 to 229 s and the value of peak responsivity increases by about three orders of magnitude as the film is exposed to air for about 10(6) s. On application of MgO capping layer, the decay time of the photocurrent marginally increases from approximate to 0.2 to approximate to 0.4 s and the value of peak responsivity increases only by one order of magnitude over the span of 10(6) s, thereafter showing tendency of saturation, implying much better stability in performance. The MgO capping layer is transparent to UV, but acts as a diffusion barrier for oxygen, stabilizing the UV photoresponse.