Modulation Of WSe₂-based Van Der Waals Structures Interface Carrier For Construction Of Their Photoelectric Devices

With the development of optoelectronic devices towards miniaturization,higher performance,and intelligent,traditional semiconductors are facing enormous challenges.As a typical representative of two-dimensional ambipolar materials,the WSe2 offers excellent application potential in next-generation optoelectronics due to its ambipolar features for gate-tunable carrier type,appropriate bandgap,high carrier mobility,and intense light absorption capability.In this thesis,high-quality monolayer and few-layer WSe2 are fabricated with the optimized synthesis factor.The modulation mechanism for carrier behaviour in WSe2 by piezopotential on the interface of WSe2/ZnO van der Waals(vdWs)heterostructures is systematically elucidated.The photosensor with enhanced photoresponse performance is constructed with WSe2/ZnO vdWs heterostructures.The influence mechanism for carrier behaviour in WSe2 by metal's work function on metal/WSe2 vdWs interface is demonstrated.A WSe2 homojunction is constructed,and their carrier type and concentration are modulated by an external gate.Finally,a polarity-reversible homodiode is fabricated.Monolayer and few-layer WSe2 are fabricated by chemical vapor deposition with optimized synthesis process.The halide-assisted reaction mechanism for fabricating WSe2 on atmosphere condition is revealed.Through systematic investigations,the influence of the structural stability is the concentration of H2 and the critical points for controlling layer number of WSe2 is the growth temperature and time.Besides,the high-temperature-assisted and metal-assisted mechanical exfoliation methods are developed for fabricating 2D WSe2.WSe2/ZnO mixed-dimensional vdWs heterostructures are designed and constructed.The modulation mechanism for carrier behavior in WSe2 by local piezoelectric field at the WSe2/ZnO vdWs interface is revealed comprehensively.The enhancement mechanism for the photocarrier separation efficiency of WSe2 by the tensile strain induced positive piezopotential is exlusided.A WSe2/ZnO photosensor is fabricated with self-powered photoresponse and enhanced photoresponsivity from 117 mA/W to 394 mA/W under 0.87%tensile strain.The metal/WSe2 vdWs heterostructure is designed and constructed.The modulation mechanism of interface carrier behaviour of vdWs heterostructure by different metal work function is presented.The influence on the carrier type in WSe2 by metal work function is revealed clearly.The hole-dominated carrier transport is emerged on the metal/WSe2 interface with higher work function than the Fermi level of WSe2,while the electron-dominated carrier transport is arised on the metal/WSe2 interface with lower work function than the Fermi level of WSe2.A WSe2 homojunction is designed and fabricated.The modulation mechanism for the carrier type and transport in WSe2 by external gate modulation is elaborated.The influence on the change of rectifying polarity in WSe2 homojunction by the gate screening effect of the local electrode structure was investigated.The WSe2 homojunction diode is fabricated and displays excellent rectifying behaviour with a rectification ratio over 105 and photovoltaic performance(90%external quantum efficiency and 2.3%power conversion efficiency)under gate voltage modulation.Notably,the short-circuit current and open-circuit voltage of diode can be easily reversed from positive to negative state.By using this reversible characteristic,a new-brand logical optoelectronic switch is achieved.