Electric-field effect of near-band-edge photoluminescence in bulk ZnO

We have studied the effect of electric fields on the near-band-edge (NBE) emissions in bulk zinc oxide (ZnO) by using photoluminescence and photocurrent (PC) spectroscopy simultaneously. The intensity-quenching and peak-shift effects of the free exciton spectra were observed with increasing electric field. From the PC result, we find out that the free excitons are disturbed by the PC carriers of the photo-created electrons and holes. This disturbance reduces the recombination ratio and the lifetime of free excitons. Therefore, the intensity-quenching effect was attributed to the decrease in the recombination of free excitons. Thus, the shift of the free exciton peaks was related to Stark effect induced by electric field. As a result, we have found that these phenomena are caused to the exciton–electron scattering due to a strong interaction between the excitons in the conduction band and the photo-generated electron carriers with increasing the applied electric field.