Increasing Photo/dark Current Ratio Of ZnO Ultraviolet Detector Using Self-polarized BaTiO₃ Ferroelectric Thin Films

Ultraviolet?UV?detectors have potential application value in many areas such as optical communication,environmental monitoring and space research.It is urgent to design and fabricate high-performance UV detectors.Ferroelectric material is a new type of functional materials which have been introduced to UV sensors to regulate the performance of UV detectors.The ferroelectric domains are uniformly oriented when the ferroelectric thin film is polarized by an external electric field.The surface polarization charges produce an electric field which reduces the carrier concentration of the semiconductor.Consequently,the dark current of the UV detector is significantly reduced,and the photo/dark current ratio is improved.However,the polarization process makes the preparation process of the device complicated.Because of this defect,this paper starts from the structural aspect,and uses the self-polarized ferroelectric thin film as the ferroelectric control layer,to reduce the dark current of UV detectors and increases the photo/dark current ratio of UV detectors without external electric field polarization.Compared with the Zinc Oxide?ZnO?ohmic-contact device on the SiO₂/Si substrate,the dark current decreases by about two orders of magnitude,and photo/dark current ratio is increased by about two orders of magnitude,when the self-polarized BaTiO₃ thin film acts as a ferroelectricgated layer.This device structure not only improves the UV detection performance of ZnO,but also requires no external electric field to polarize ferroelectric thin film.And thus this kind of UV detector becomes more practical.The structure of this device shows good stability.Since the ZnO ohmic-contact device can maintain the high photo/dark current ratio?799?and the domain in BaTiO₃ ferroelectric thin film does not change obviously after 100 days.The domain arrangement has obvious orientation.When the Schottky barrier and the electric field generated by the BaTiO₃ ferroelectric thin film are present,the dark current of the ZnO unidirectional Schottky-contact device is reduced to 8fA and the photo/dark current ratio can reach 9.5×10⁶.The photo/dark current ratio of the unidirectional Schottky-contact device on the self-polarized BaTiO₃ thin film is about four orders of magnitude higher than the photo/dark current ratio of the ohmic-contact device self-polarized ferroelectric thin films.This conclusion provides a new idea for the fabrication of high photo/dark current ratio UV detectors,namely designing and fabricating UV sensors that utilize ferroelectric field and Schottky barriers simultaneously.