The Self-powered Uv Photodetector Based On P-NiO Heterostructure P-n Junction

Ultraviolet photodetector is a kind of device which converts incident ultraviolet signal into electric signal by photoelectric effect.It has important application in people's livelihood and military field.Conventional ultraviolet photodetectors usually use Si as photosensitive materials.Because of its small band gap,it needs additional filters to realize ultraviolet detection,and the false alarm rate is high.At the same time,such photodetectors often need external bias to work,which undoubtedly increases the size of the device is not conducive to the future development trend of miniaturization and integration.The absorption edge of the third generations semiconductor material with a band gap greater than 3.0 e V directly corresponds to the ultraviolet region,which can be detected without a filter,greatly improving the accuracy of the photodetector.Due to the built-in electric field formed in the junction area of the photodetector based on p-n junction structure,the photogenerated charge carriers can be separated spontaneously so as to realize the function of self-powered detection,which can greatly reduce the size and cost of the device.NiO is a natural p semiconductor material with a band gap of 3.6 e V,the absorption edge is 345nm.Good photoelectric performance,excellent visible light transmittance and thermochemical stability make it very suitable for other n-type semiconductors together construct a self-powered ultraviolet photodetector.In this paper,the growth conditions of NiO thin films were investigated by magnetron sputtering method,and the optimal parameters were obtained.Then,NiO/GaN and NiO/Ga₂O₃ heterostructure were constructed by combining with GaN and Ga₂O₃materials,respectively.The details are as follows:1.Controllable growth of NiO film.Magnetron sputtering was used to explore the growth of NiO films on sapphire substrates.The effects of growth conditions such as substrate temperature,oxygen-argon ratio,and sputtering power on the crystallization,optical,and electrical properties of NiO films were studied and summarized.The experimental results show that when the temperature is higher than 200?,the film exhibits good crystalline properties along the(111)crystal plane.Meanwhile,as the temperature increases,the crystallinity and the resistivity of the film increases.The ratio of oxygen to argon affects the content of Ni vacancies in the film and thus the conductivity of the film.As the oxygen content increases,the Ni vacancies in the film increase and the conductivity increases.The sputtering power affects the film thickness and crystallinity.As the sputtering power goes up,the film become thicker and then become thinner,while the film crystallinity becomes better first and then worsens;2.Self-powered ultraviolet photodetector based on NiO/GaN heterostructure p-n junction.On the basis of the above-mentioned research results,a layer of NiO film with a thickness of about 70 nm and preferentially grown along the(111)crystal plane was deposited on the GaN thick film by magnetron sputtering.A self-powered ultraviolet photodetector was obtained by making an electrode.The device exhibits typical rectifying characteristics with a rectifying ratio of>10² at±0.5V.Due to the presence of the built-in electric field,the photodetector can work without an external bias voltage.Under zero bias,the photodetector shows a detectivity up to 2.83×10¹⁴ Jones for 365 nm ultraviolet light,which is the best in the current self-powered ultraviolet photodetector based on NiO materials.At the same time,the responsivity is 272.3 m A/W,second only to the previous reported 290 m A/W,and the response speed reaches 31 ms.These excellent properties show that NiO/GaN p-n junction ultraviolet photodetector have very good application prospects in UV-A detection fields such as UV curing monitoring and forest fire monitoring.3.Self-powered solar-blind ultraviolet photodetector based on NiO/Ga₂O₃heterostructure p-n junction.NiO film(4?m thick)and Ga₂O₃ film(200 nm thick)were deposited on sapphire substrate by magnetron sputtering at room temperature to form a NiO/Ga₂O₃ p-n junction,and graphene was transferred on Ga₂O₃ layer as an electrode to construct a solar-blind ultraviolet photodetector with self-powered performance.The results show that the device exhibits a responsivity of 57?A/W to 100?W/cm² of 254 nm ultraviolet light under a 0 V bias,and a detectivity of 5.45×10⁹ Jones,with a light-dark current ratio of 122 and a response speed of 0.34 s.Then,the light response characteristics of the photodetector were compared and tested in air,oxygen,and vacuum environments.The results of this chapter show that NiO/Ga₂O₃ heterostructure p-n junction ultraviolet photodetector are very suitable for detection in the UV-C band,and can be used in ultraviolet light sterilization dose detection,ozone layer hole monitoring and other fields.