Optical properties of polar thin films: ZnO (0001) and ZnO (000–1) on sapphire substrate

In this paper, the optical properties of ZnO (0001) and ZnO (000–1) films were systematically studied. ZnO polar films were deposited on sapphire substrates by Molecular beam epitaxy (MBE). The morphology, structure and optical properties of the ZnO polar films were measured by atomic force microscopy (AFM), X-ray diffraction (XRD), photoluminescence spectra (PL), absorption spectra and spectroscopic ellipsometry (SE), and the results show that the bandgap obtained by SE was consistent with that obtained by absorption spectrum. Moreover, compared with ZnO (000–1) films, the optical bandgap appears red shift on ZnO (0001) films, which may be caused by impurity states near the bottom of the ZnO conduction band.