Effects of near-surface defects on the optical, electrical and magnetic properties of ZnO films

We studied the optical, electrical and magnetic properties of ZnO films prepared by using a pulsed laser deposition method. Low-temperature photoluminescence (PL) measurements revealed a strong emission line at 3.333 eV. A dependence of this emission intensity on oxygen adsorbed on the surface was observed, indicating a near-surface origin for the emission. The transition at 3.333 eV was attributed to bound exciton, and the observed anomalously small thermal activation energy in comparison with the localization energy could be explained by a modification of the surface state. The observed resistance switching effect and ferromagnetism in the ZnO films were related to the existence of defects responsible for the PL emission at 3.333 eV.