Study On The Performance Of Two-dimensional PdSe₂ Film Van Der Waals Heterojunction Ultraviolet Photodetectors

Ultraviolet（UV）photodetectors are widely used in military and civil fields,such as national defense warning,environmental monitoring,industrial production,medicine and health care.Current UV photodetectors are mainly based on a single wide bandgap semiconductor material.These materials generally have good thermal conductivity,high breakdown electric field,low dielectric constant,high radiation resistance and an inherent appropriate band gap,which make them suitable for UV photodetection.The UV photodetectors based on wide bandgap semiconductor have the advantages of small size,low operating voltage,low energy consumption and long service life.However,due to the lack of effective carrier separation mechanism,UV photodetectors based on single wide bandgap semiconductor material have certain limitations in the application of photodetection,such as the need for external power supply,slow response speed and other shortcomings.Two-dimensional transition metal dichalcogenides（TMDs）,especially palladium diselselenide（PdSe₂）,have attractive physicochemical properties such as dangling-bond-free surface,high carrier mobility,adjustable band gap and good chemical stability.In addition,it has the characteristics of in-plane anisotropy and angle dependence of absorption spectrum.These characteristics lay a foundation for it constructing van der Waals heterojunction with wide bandgap semiconductor materials to achieve high performance UV photodetection and polarization detection performance.In this paper,a van der Waals heterojunction UV photodetector based on two-dimensional PdSe₂ thin film and wide bandgap semiconductor materials（gallium nitride（GaN）and gallium oxide（Ga₂O₃））was constructed by in-situ van der Waals growth method,and its photoelectric properties and applications were studied.The main research contents and results are as follows:1.Wafer-Scale two-dimensional PdSe₂ films were prepared by van der Waals growth method.Then a series of characterization tests were carried out to evaluate the film quality.The results show that two-dimensional PdSe₂ film with large area and high crystal quality has been synthesized.2.The PdSe₂/GaN van der Waals heterojunction UV photodetector was constructed,and its photoelectric performance was tested and analyzed.Due to the high quality of the heterojunction,the device can realize self-driven photodetection.High responsivity（R）of 249.9 m A/W,specific detectivity（D*）of 7.9×10¹² Jones and fast response speed can be achieved under 0 V bias and 360 nm illumination.The high UV/Visible rejection ratio of 2.2×10³ can be achieved at zero bias voltage.More importantly,due to the folded low-symmetry pentagonal crystal structure of PdSe₂ film,the device is highly sensitive to polarized UV light with a large dichroic ratio up to 4.5.These findings further demonstrate the excellent polarization UV photodetection performance of PdSe₂/GaN van der Waals heterojunction and its potential for polarization imaging and secure UV communication.3.β-Ga₂O₃ and Sn:Ga₂O₃ with different Sn doping ratios were synthesized by chemical vapor deposition（CVD）method,and then the crystallization quality and chemical properties were evaluated by a series of characterization methods.The results show that Ga₂O₃ and Sn:Ga₂O₃ films with high crystalline quality have been successfully synthesized.4.Design and construct Ga₂O₃ and Sn:Ga₂O₃ based UV photodetectors,and then study the influence of doping ratio on their photoelectric properties.By comparison it is found that when the doping ratio is 50:1,the UV photoelectric detection performance is relatively good,and the responsivity of 303.12 m A/W,specific detectivity of1.87×10¹² Jones and external quantum efficiency of 153%can be achieved at 245 nm and 5 V bias voltage.Based on this,the PdSe₂/Sn:Ga₂O₃ van der Waals heterojunction UV photodetector was constructed by 50:1 doping ratio of Sn:Ga₂O₃ and two-dimensional PdSe₂ film,and its photoelectric performance was studied.The values of R,EQE and D*at 0 V bias and 245 nm are 3.9×10^-2 m A/W,0.02%and 2.56×10¹⁰ Jones,respectively,realizing self-driven deep UV photodetection.