Study On TMDs-based Mixed-dimensional Heterojunction Ultraviolet Photodetectors

Recently,ultraviolet（UV）photodetectors have been widely studied for their important applications in military and civilian such as flame detection,missile warning,security communications,marine oil pollution monitoring,and biomedicine.At present,most commercial UV photodetectors are vacuum photomultipliers and Si-based photodiodes.They also have some disadvantages,such as large volume,high power consumption,heavy weight and low reliability,which limit their further application and development.Therefore,it is necessary to explore new materials and design new devices to prepare a new type of high-performance UV photodetector,so that it will develop towards higher accuracy,lower energy consumption,and smaller size than before.With the continuous development of semiconductor materials,wide-bandgap semiconductor such as gallium nitride（Ga N）and gallium oxide（b-Ga₂O₃）have played an important role in the UV detection because of their large optical absorption coefficient,high chemical stability and thermal stability.On the other hand,the emergence of two-dimensional transition metal dichalcogenides（TMDs）with many excellent characteristics,such as good mechanical flexibility,dangling-bond-free surface,excellent chemical stability,good integration compatibility,high carrier mobility and tunable electronic properties,etc.,provides a new platform for the realization of high-performance UV photodetection.However,due to the significant exciton effect of the two-dimensional materials,the separation of photo-generated carriers is obviously hindered,thereby limiting the performance of the device.In addition,the two-dimensional materials obtained by the mechanical cleavage are of high quality,but their size are Small,And they are poor controllability and reproducibility.As a result,the later device preparation process is complicated,and it is not suitable for preparing array and integrated devices.In order to overcome these shortcomings of two-dimensional materials,we combine two-dimensional materials with traditional wide-bandgap semiconductors（Ga N,b-Ga₂O₃）to construct two-dimensional/three-dimensional（2D/3D）mixed-dimensional vertical structure,which can achieve enhanced light absorption and improve the separation efficiency of photo-generated carriers,so as to achieve the purpose of high-performance UV detection.In addition,the preparation process of the 2D/3D structure is simple,and the selection of3D wide bandgap semiconductor materials is diverse,which is conducive to achieving good UV spectral selectivity.For the preparation of two-dimensional materials,we adopt the metal-sulfur/selenization method,which is simple,controllable and repeatable,and can synthesize continuous and uniform two-dimensional samples in large area.The research findings are as follows:1.Two-dimensional tungsten disulfide（WS₂）and platinum diselenide（PtSe₂）films were synthesized by metal-sulfur/selenization method.That is,the metal W and Pt films are deposited separately by magnetron sputtering,and they are placed in a CVD system for sulfur/selenization reactions to synthesize large-area two-dimensional WS₂ and PtSe₂ films.Then the synthesized two-dimensional films were characterized,and the analysis and characterization results showed that the continuous,uniform,and large-area two-dimensional WS₂ and PtSe₂ films with high crystalline quality were successfully synthesized.2.The WS₂/Ga N 2D/3D mixed-dimensional heterojunction UV photodetector was designed and constructed,and its photoelectric performance was tested and analyzed.The device has a significant photovoltaic effect(V_OC=1.73 V,I_SC=3.18mA)under 375nm UV illumination,making it self-driving.At the same time,the device exhibits excellent UV photodetection performance,with a high responsivity of 226 m A/W under 0V bias,an ultra-high detectivity of 4×10¹⁴ Jones,and a fast photoresponse.In addition,the WS₂/Ga N heterojunction photodetector can be used as an UV imaging sensor to obtain high-contrast,high-resolution UV image.3.Graphene（Gr）/PtSe₂/b-Ga₂O₃ 2D/3D Schottky junction solar-blind deep ultraviolet（DUV）photodetector was designed and constructed.The Gr is used as a transparent electrode to improve the collection efficiency of carriers,improving the response speed of the device.The device exhibits excellent performance,with high responsivity of 76.2 m A/W and detectivity of 1.93′10¹³ Jones under 245 nm DUV illumination,a high current on/off ratio of～10⁵,and an ultra-fast response speed of 12ms/503.4ms.In addition,the UV/Visible rejection ratio of the device is as high as1.8′10⁴.The photodetector can also be used as a single-pixel imaging sensor to obtain high-resolution images.These results indicate that Gr/PtSe₂/b-Ga₂O₃ Schottky junction devices have great prospects in high-performance self-driven solar-blind DUV photodetection and image sensing.