Atmosphere-Dependent Photoconductivity of ZnO in the Urbach Tail

Figure 8

The comparative results between (a) time decays and (b) photoconductive responses in air, inert atmosphere and vacuum conditions with light excitation above and below ZnO bandgap. (c) In an air atmosphere, an oxygen photodesorption occurs when the excitation is above bandgap due to free hole concentration in valence band. (d) When the excitation is below bandgap, the oxygen photodesorption process is suppressed. The main effect of excitation in the Urbach tail is the decrease of photodesorption causing the increase of photoconductivity decay times.