Research On Novel Photodetectors Based On WSe₂ Homojunction

Since British scientists Gaim and Novoselov successfully prepared single-layer graphene by mechanical exfoliation in 2004,other two-dimensional layered materials have also been discovered and synthesized.Two-dimensional layered materials have strong quantum size effects,high carrier mobility,and atomic layer thickness,and exhibit physical and chemical properties that are quite different from those of bulk materials,so they have received extensive attention from many scholars.However,the zero-bandgap structure of graphene leads to high electron concentration and large dark current,so there are certain limitations in the application of optoelectronic devices.Therefore,scientists have turned their attention to transition metal dichalcogenides(TMDCs)with tunable band gap(1-2 e V)structures,which can make up for the shortcomings of graphene's zero band gap and can be better applied to semiconductor devices.With the deepening of research,the family of two-dimensional materials has become increasingly large,and there are more than700 two-dimensional materials with a thickness of atomic layers that can exist stably.The rise of the wave of two-dimensional materials not only brings new opportunities,but also makes people face certain challenges before traditional craftsmanship.As a representative of transition metal chalcogenides,tungsten diselenide(WSe₂)has unique bipolar properties,such as high carrier concentration,high carrier mobility,and room temperature stability.Based on WSe₂materials,this paper has done the following work:1.A photodetector based on Au-WSe₂-Au back-to-back Schottky structure was fabricated by mechanical exfoliation and standard micro-nano process,and the device exhibited excellent optoelectronic properties at room temperature such as low dark current(10^-11A),High responsivity(10⁵A/W)and wide response band(450-1060 nm).At 830 nm,the photoelectric response of the device was tested by modulating the incident laser power density,which verifies the detection capability of the device under weak light(0.35 n W)conditions.In addition,this work demonstrates that the photoresponse mechanism of the device can be regulated by bias voltage,and the exponential relationship between photocurrent and power indicates that the dominant photoresponse mechanism shifts from the photovoltaic effect to the Photogating effect.The photocurrent exhibits a stable and fast spectral photoresponse in the wavelength range of 450 nm-1060 nm,which indicates that the device has potential applications in the visible light and near-infrared fields,and is also useful for the development and application of two-dimensional materials in high-sensitivity photodetection.Application provides a feasible way.2.Based on the property that the band gap of WSe₂changes with the number of layers,a thick and thin layer of WSe₂in-plane homojunction was fabricated by mechanical exfoliation.In the experiment,the position of the Fermi level of the back gate is adjusted by changing the voltage,and the homojunction is transformed from an N-N junction to a P-P junction.We apply this feature to digital circuits.In addition to being an electronic device,the device also has excellent performance as an optoelectronic device.We tested the output characteristic curves of the device at different power densities under the illumination of incident light with a wavelength of830 nm and a wavelength of 637 nm,and also calculated the responsivity and detection rate of the device at different wavelengths.The performance of the base diode is comparable,which is a further step for us to explore the preparation and application of optoelectronic devices in the future;The experiment also used intrinsic WSe₂crystal to obtain a natural step-like in-plane p-n junction device by mechanical exfoliation,which has a low dark current(10^-13A)at room temperature and photocurrent switching at 520 nm wavelength.than about 10⁸.We also tested the photoresponse at wavelengths of 450 nm-940 nm,demonstrating its detection capability under weak light(as small as 0.34 n W)and a broad spectral photoresponse.