Persistent photoconductivity in ZnO nanostructures induced by surface oxygen vacancy

ZnO nanowall networks grown on SiO2/Si substrate were found to exhibit persistent photoconductivity (PPC). The relaxation rate of the persistent photocurrent is enhanced by a higher oxygen level in the ambient suggesting that PPC is closely related to the ZnO surface. Surface modification with hydrogen peroxide can significantly reduce the PPC relaxation time, implying that surface oxygen deficiency is responsible for the effect. The transition between the neutral and the metastable singly ionized states of the surface oxygen vacancy is suggested to account for the phenomenon and it is supported by the temperature and wavelength dependence of the PPC. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)