Characterization of UV-modulated dielectric constant of ZnO thin films

The modulation on complex dielectric constant of ZnO thin film with ultraviolet (UV) light is investigated by common-path heterodyne interferometer in visible range. The results indicate that the dielectric constant of ZnO thin film is reduced under UV irradiation. The dielectric constant recovers when the UV irradiation vanishes. As the dielectric constant is related to the charge density of bounded electrons, or so-called valence electrons, the influence of UV irradiation on the resistance of ZnO thin film was studied to clarify the physical mechanism associated with the UV-modulated dielectric constant. It was observed that a smaller resistance was achieved for ZnO thin film under UV irradiation. This implies that the valence electrons absorb the irradiated UV and become conduction electrons.