Self-powered Photoresponse Characteristics Of ZnO/Cu₂O Heterojunction Photodetector And Its Application

Photodetectors(PDs)are the devices that convert optical signals into electrical signals,and widely used in various fields of military,national economy and life.In order to meet the development needs of the Internet in the future and welcome the arrival of the era of artificial intelligence,the technology of realizing high-speed transmission of information using light as the information transmission medium and PDs as the signal receiving terminal has attracted widespread attention.The PDs have been required the high performance and multi-function for the applications.The rapid development of ultra-high-speed optical communication,signal processing,measurement and sensing systems requires high sensitivity,fast response speed,low energy consumption and easy integration of PDs to meet applications in various fields.The tunable bipolar binary light response characteristics of the heterojunction PDs(changes in positive and negative current values)can be used to realize the applications such as optical communication,optical information storage,and optical multi-logic circuit operation.In this paper,a Zn O/Cu₂O heterojunction PD with photovoltaic effect was prepared,which exhibits fast and broad-spectra response characteristics to ultraviolet light and visible light.The bipolar binary light response can realize under the cooperation of light field and electric field.The self-powered photoresponse characteristics of the Zn O/Cu₂O heterojunction PD is enhanced by improving the hole transport ability of Cu₂O film,reducing the carrier recombination centers.The main research content and conclusions of the thesis are as follows:(1)The polarity and magnitude of the current of the heterojunction PD under illumination depend on the competition between the photogenerated current(I_p)and the junction current(I_j,the difference between the diffusion current and the drift current)in the opposite direction in the heterojunction.By adjusting the light field and electric field,the Zn O/Cu₂O heterojunction PD obtains an output current with controllable polarity and realizes a binary light response characteristic.When a small external bias voltage(0 V<V_bias<V_oc)is applied,the photogenerated current of the heterojunction can be adjusted by changing the light wavelength and intensity.When the photogenerated current is greater than the junction current,the device can realize the current polarity conversion during optical switching.When the applied bias voltage is larger(V_bias>V_oc),the junction current of the device is larger,and the device current only changes in numerical value during optical switching,and the polarity does not change.The heterojunction device presents two current states under the action of different light fields and electric fields,which can realize the conversion of optical signals and digital signals and the programmable processing of digital signals.The research results provide an example for realizing the bipolar binary light response of a heterojunction PD with photovoltaic effect by adjusting the light wavelength,light intensity and applied bias voltage.(2)The crystalline quality of Cu₂O film affects the photoelectric response characteristics of Zn O/Cu₂O heterojunction PDs.The Na₂EDTA surfactant is added into the electrolyte to adjust the growth process of low-temperature electrochemically deposition.The polycrystalline structure of Cu₂O film is changed to a single crystal-like structure with the preferential oriented growth along(111)crystal plane,which can reduce the grain boundary trapping and the loss of photo-generated carriers,and then improve the transmission ability of photo-generated carriers.The photocurrent value reaches 7.3×10^-5A and the light sensitivity is 1.17×10¹³Jones under 470nm light illumination without applied bias.Due to the self-driving ultraviolet(UV)-visible dual-band photoresponse characteristics,the Zn O/Cu₂O heterojunction device is applied to the“OR”gate of the UV-visible dual-band optical control digital logic circuit.The UV light and visible light can be encoded in dual bands,and the heterojunction device can realize the detection of visible light signals encrypted by UV light.The heterojunction PD helps to improve the security of visible light communication.(3)The carrier transport characteristics of Cu₂O film will affect the photoelectric response performance of Zn O/Cu₂O heterojunction devices.Cu_xS particles are embedded in the Cu₂O film through the vulcanization treatment of the Cu₂O film.Utilizing the high conductivity of Cu_xS,the transmission and collection ability of photo-generated holes of heterojunction devices are improved,the recombination of carriers is reduced,and the UV light response performance of the devices are improved.The photocurrent of the vulcanized heterojunction device increases and reaches 3.4×10^-6A for the PD with 75 s vulcanization treatment under 365 nm illumination without applied bias.