Preparation And Properties Of Molybdenum Disulfide And Its Heterojunction Photodetector

Since the discovery of two-dimensional layered materials,they have received extensive attention from researchers because of their excellent performance in electricity,light,heat and force.Different from graphene which has zero band gap structure,MoS₂has a natural band gap,and its conductive property belongs to the semiconductor type,so it has great potential application values in the field of micro-nano optoelectronic devices.In the field of photodetection,MoS₂ has a higher light absorption rate and a wide spectral absorption range,and so it is suitable for usage in photodetectors.At the same time,it has been found that the layered atomic structure of MoS₂-like materials can be stacked together like the stacking of Lego bricks to form two-dimensional van der Waals heterojunctions.Different combinations of heterostructures not only sustain the properties of a single material,but also produce new physical properties under synergistic effect,resulting a composite optoelectronic device with multiple functions.In this paper,the mechanical stripping preparation method of MoS₂ was firstly explored,and the effects of stripping process on the thickness and surface morphology of MoS₂ nanosheets were studied.On this basis,the MoS₂/Si heterojunction photodetector and MoS₂/GaSe heterojunction photodetector were prepared by controlled stripping of multilayer MoS₂ nanosheets and precise micro-transfer method.The energy band structure and photoelectric properties of the two type of heterojunctions were studied.The main research contents include:?1?For the weaker light absorption rate and smaller light absorption cutoff wavelength?670 nm?of single-layer MoS₂,MoS₂/Si heterojunction photodetector was prepared by mechanical stripping method and maskless direct laser writing technology.The test results show that the spectral response range of the heterojunction is 450-980nm,and it has a higher response rate and better stability to the laser of 980 nm wave length.The switching ratio of the device can reach 8×10⁴,and the response time can be as fast as 150 us,which is approximately 10 times faster than that of previously reported devices,mainly due to the application of an electric field perpendicular to the interface of the heterojunction.?2?The precise alignment and stacking of small size two-dimensional materials are realized by self-built micro-displacement operation system,and a MoS₂/GaSe Van der Waals heterojunction photodetector is fabricated.The strong interlayer coupling between MoS₂ and GaSe was observed by Raman spectroscopy.At the same time,the photoelectric properties of the heterojunction were studied and its wide wavelength response range was demonstrated.The optical response cut-off wavelength was wider than that of the pure multilayer MoS₂ and GaSe.The optical response to 980 nm laser was detected,which was caused by type II interlayer excitation of the van der Waals heterojunction.The device has the highest response rate to 635 nm laser under the same incident power with a response time of 32 us and a weaker response rate to 980 nm laser with a response time of 40 us.Finally,the band structure of the heterojunction is plotted,and the physical mechanism of the photoelectric response of the heterojunction is explained.It is proved that the van der Waals heterojunction with type II atomic layer structure can realize interlayer excitation,which is valuable for further research in photoelectric detection.