Persistent Photoconductivity in ZnO Nanowires in Different Atmospheres
Figure 5
(a) The photogenerated electrons and holes in a ZnO nanowire are separated due to the built-in electric field cause by the band bending. The life-time of the pair is thus increased and the photoconductivity rises fast; (b) as the excitation process continues, the energy barrier at the surface lowers and oxygen molecules can readsorb. This leads to an equilibrium between adsorption and readsorption and as a consequence the photo-current saturates. In both figures, the color of photogenerated-carriers is blue, whereas other electrons in the conduction band determine the intrinsic n-type conductivity of ZnO and are indicated in black. The green arrows describe the retrapping of electrons and the oxygen readsorption.
