Study Of Two-dimensional WSe₂,MoS₂ Field-effect Transistors And Photodetectors

Photodetectors,as an important part of modern optoelectronic technology,are at the forefront of modern optoelectronic and microelectronic technology,and are widely used in military and civilian products.The band structure and band gap of the semiconductor affect the figure-of-merits of photodetector,such as photoreponsivity and detection range.As the traditional silicon photodetectors are based on indirect bandgap semiconductor,which limits the light absorption efficiency.Two-dimensional（2D）transition metal disulfides have tunable band gaps,and their energy band structures and band gaps change with the thickness of the materials,thus providing an opportunity to realize high-performance photodetectors.However,the deposition of metals by conventional thermal evaporation methods can damage the semiconductor lattice structure and cause interfacial defects,resulting in high Schottky barriers at the metal-semiconductor interface,limiting the photocurrent of the photodetector.To solve the problem,in this paper,a material transfer method was used to form van der Waals contacts at the metal-semiconductor interfaces,and a suspended structure was used to redeuce interfacial defects,with the following main studies:1.The dependence between the energy band structure and the layer numbers of common two-dimensional materials（WSe₂,MoS₂）was investigated,and the band offset parameters of the some two-dimensional heterojunctions were measured.The two materials are characterized by photoluminescence spectroscopy and Raman spectroscopy,and the differences in photoluminescence spectra as well as Raman spectra of MoS₂ with different layer numbers are analyzed.As the layer number increased,the A peak in the photoluminescence peaks of MoS₂ redshifted（related to the direct band gap transition at the K point）,and₂₂¹)peak in the MoS₂ Raman spectra redshifted while the₁₂)peak blueshifted.The ReS₂/WSe₂ and ReS₂/MoSe₂heterojunctions were prepared,and then the heterojunctions were characterized using X-ray photoelectron spectroscopy to calculate the band alignment parameters of the heterojunctions.The results showed that ReS₂/MoSe₂ is a type-I heterojunction and ReS₂/WSe₂ is a type-II heterojunction.2.The relevant electronic devices and optoelectronic devices were prepared based on 2D MoS₂ and 2D WSe₂.The performance differences between the suspended WSe₂devices and the substrate-supported WSe₂ devices were compared.The suspended devices exhibited a hole mobility of 0.23 cm²/（V·s）and a subthreshold swing of 485m V/dec,while the substrate-supported devices exhibited a hole mobility of 1.13cm²/（V·s）and a subthreshold swing of 667 m V/dec.3.Then the optoelectronic properties of the suspended and the substrate-supported WSe₂ devices were tested,and optoelectronic properties of MoS₂ photodetectors were studied.Two WSe₂ devices showed good response in the visible wavelength range,and the responsivity of the suspended WSe₂ photodetector was improved compared with the conventional substrate-supported type.Specifically,the responsivity of the suspended WSe₂ photodetector and the substrate-supported WSe₂ photodetector were30.4 A/W and 3.2 A/W,respectively,at 532 nm laser illumination and a power density of 105.36 W/m²(V_GS=-60 V).Besides,the suspended structure reduces the effect of traps from substrate,thus maintaining fast response speed.