Photoluminescence properties of ZnO thin films grown by electrochemical deposition

We have investigated the photoluminescence properties of ZnO thin films grown by electrochemical deposition. By applying a thermal treatment at 500degreesC in O-2 atmosphere, a free-exciton photoluminescence is observed. Furthermore, under high-density excitation conditions, a photoluminescence band appears on the low-energy side of the free exciton. The photoluminescence intensity exhibits an almost quadratic dependence on the excitation power, and the energy spacing between the photoluminescence band and the free exciton is almost equal to the exciton binding energy of ZnO. We conclude from the above results that the photoluminescence band under high-density excitation conditions originates from an inelastic scattering process of excitons, the so-called P emission.