Photoluminescence spectra of nano-structured ZnO thin films

The nano-structured ZnO thin film has been grown by molecular beam epitaxy on an Si (1 0 0) substrate. The emission spectra of ZnO samples were measured with the photon counting method in the temperature range from 18 to 140 K by using the synchrotron radiation up to the vacuum ultraviolet region. Under the excitation of 196 nm, two main emission bands have been observed, which peak at 330 and 430 nm approximately. The 330 nm emission band is due to the radiative recombination of excitons in surfaces associated with the O 2p dangling-bond state, and the 430 nm band is attributed to the deep-level emission, which is related to oxygen vacancy defects. The temperature dependence of these two emission bands and the influence of the sample's annealing on the emission spectrum support our suggestions about the origin of the 330 nm emission band as well as the 430 nm one.