Study On Broadband Photodetectors Based On 2D TMDs/Ge Van Der Waals Heterojunctions

Since the mechanical stripping of graphene in 2004,two-dimensional(2D)nanomaterials have entered a period of rapid development.2D nanomaterials have attracted the research interest of many scholars due to their atomic-level thickness,van der Waals force stacking,and free of suspension bonds on the surface.At present,2D materials have been successfully synthesized,including black phosphorus(BP),boron nitride(BN),transition metal dichalcogenides(TMDs),etc.The diversity of electronic structure of these materials provides a new approach for basic scientific research.As a typical 2D material,TMDs has the characteristics of high carrier mobility,excellent chemical stability and layer-dependent tunable band-gaps,etc.TMDs is an ideal material for preparing optoelectronic devices.As a newly discovered TMDs,Palladium disselenide(Pd Se₂)gradually reduces its band gap from 1.08 e V in monolayer film to0 e V in bulk with the increase of the number of layers,and changes from semiconductor to semi-metal material.In addition,its wrinkled pentagonal asymmetric crystal structure makes Pd Se₂ strongly anisotropic,so it can be used for polarized light detection.In addition,the defect engineering can effectively reduce the band gap of tungsten disulfide(WS₂),thus providing a good material foundation for the realization of broadband infrared detection.Although 2D TMDs photodetectors have many advantages,they still have some disadvantages.At First,due to their ultra-thin properties,the absorption of incident light is limited,which is far less than that of three-dimensional semiconductor materials.Secondly,the large exciton effect in TMDs hinders the collection and separation of the carrier.In addition,the current preparation processes mostly adopt physical or chemical vapor deposition method,etc.,which has poor preparation controllability and small transverse size of materials(mostly micron),leading to complex device construction.These deficiencies seriously hinder the large-scale application and development of 2D TMDs materials in the field of photodetection Therefore,we studied and designed a large area synthesis process for 2D TMDs materials,and constructed a hybrid dimensional van der Waals heterojunction device to achieve high performance photodetection.Based on the above analysis,large-area 2D Pd Se₂ and WS₂ films are prepared in this study,2D/3D hybrid dimensional van der Wals heterojunctions photodetectors are designed and constructed with Ge respectively,and the infrared photodetection performance of the devices are systematically characterized and analyzed.The main research contents are as follows.1.The inch-size large 2D Pd Se₂ films were prepared by metal selenization,and the samples were characterized by Raman,XPS and other instruments.2.The inch-size large 2D WS₂ films were prepared by thermal decomposition.The band gap of WS₂ films was adjusted by changing the sulfur vacancy concentration and the samples prepared were characterized.3.Graphene/Ps Se₂/Ge hybrid dimensional van der Waals heterojunction photodetector was designed and constructed,and its photodetection performance was systematically studied.The results show that the device has excellent infrared detection performance,with the responsivity of 691.5 m A/W,the specific detectivity of1.73×10¹³ Jones and the response speed of 6.4/92.5?s to 980 nm infrared signal under zero bias.At the same time,the device has a broadband detection from deep ultraviolet to middle infrared.In addition,the detector also shows excellent performance of polarized light detection,polarization sensitivity up to 112,which is the highest value reported so far.Based on the excellent performance of the device,we have successfully developed the function of high resolution infrared polarization imaging.This work provides a feasible strategy for the realization of high performance and polarization sensitive broadband photodetection in the next step.4.The WS₂/Al O_x/Ge hybrid dimensional van der Waals heterojunction photodetector was designed and constructed,and the photodetection performance was systematically studied.Thanks to the narrow bandgap WS₂ film induced by sulfur vacancy,ultra-thin Al O_x passivation layer and the structure of vertical heterojunction,the photodetector has the performance of high responsivity in the broadband of 200-4600 nm,and the photodetection range is one of the broadest among TMDs photodetectors.In addition,the device has good photodetection performance,with the responsivity of 634.5 m A/W,the specific detectivity of 4.3×10¹¹ Jones,the response speed of 9.8/12.7?s and good room temperature mid-infrared imaging capability.