Research On High-Performance Photodetectors Based On WSe₂/MoSe₂ Heterojunction

Photoelectric detection technology has been widely applied in civilian,industrial,and military fields such as image sensing,optical communication,healthcare,and environmental monitoring,and has irreplaceable roles and values.In recent years,novel two-dimensional optoelectronic materials,such as graphene,black phosphorus（BP）,and transition metal chalcogenides（TMDCs）have proved to be promising materials for the fabrication of next-generation high-performance photodetectors.Among them,WSe₂ and MoSe₂ materials belonging to TMDCs stand out among many novel two-dimensional optoelectronic materials due to their suitable bandgap range and environmental stability.However,due to the extremely low light absorption efficiency,the device’s optical response is low.In addition,due to the lack of suitable doping methods,the regulation of carrier concentration and the improvement of device performance are further limited.Therefore,high-quality WSe₂/MoSe₂ heterojunction phototransistors and photodiodes has been prepared in this thesis.The optical response of the device is significantly improved and doping of WSe₂ and MoSe₂ materials is achieved through photogating effect and oxygen plasma treatment.The complete optical and electrical properties of these devices are investigated,and the working mechanism of the device is analyzed in detail.The specific research content of this thesis is as follows:1.A high quality WSe₂/MoSe₂ heterojunction phototransistor is prepared.The WSe₂and MoSe₂ were used as channel layer and photogating layer respectively.The MoSe₂photogating layer can effectively capture photogenerated electrons to form a local gate,effectively modulate the conductance and hole carrier concentration of WSe₂ channel,and prolong holes lifetime with significantly improved optical gain and optical response.The experimental results show that the device has a maximum response of 1260 A/W,a maximum detectivity of 6.05×10¹² Jones,a very high external quantum efficiency of2.68×10⁵%and a fast response time of 3.5 ms.The device exhibits excellent detection performance and excellent spectral response at 405,520 and 650 nm wavelengths.2.A high quality WSe₂/MoSe₂ heterojunction photodiode is prepared and treated with oxygen plasma.The blue shift of the Raman peak of WSe₂ indicates that there is a p-type doping effect,the rectification ratio of the device is increased from 28.3 to 2236,the built-in electric field of the heterojunction is strengthened,and the p-n junction is transformed into a p⁺-n junction,which improves the separation efficiency of photogenerated carriers.In addition,due to the p-type doping effect of WSe₂,the width of Schottky barrier between WSe₂ and the electrode decreases,and the carrier tunneling probability increases,which effectively improves the photogenerated carrier transport and reduces the contact resistance.The measurement results show that the optical response of the device is greatly improved due to the enhanced built-in electric field and the reduction of contact resistance.In the self-powered mode,the short-circuit current is increased from1.38 n A to 3.57 n A,the open-circuit voltage is raised from 224 m V to 287 m V,the response is raised from 0.015 A/W to 0.033 A/W,the detectivity increases from 3.9×10⁹Jones to 7.9×10⁹ Jones,and the external quantum efficiency increases from 3.6%to 7.8%and the response time is 4 ms.