The Research On Photogating Effect In Two-dimensional Vertical Heterostructure Devices

In recent years,the two-dimensional layered materials,represented by graphene and transition metal dichalcogenides（TMDs）,have demonstrated many unique physical,chemical,electrical,optical properties,as their carriers with their migrations and heat diffusion are restricted in the two-dimensional plane.These unique properties make the two-dimensional layered materials promising candidates in the future electronics,communications,information and other fields,which have attracted wide attention from researchers around the world.In particular,the TMDs materials have exhibited many different band structures and conductive types due to their direct band gap and adjustable band gap characteristics.In the past decades,many new nano-optoelectronic devices based on TMDs layered semiconductor materials and their heterostructures have been successfully constructed,such as photodetectors,field-effect transistors,and photovoltaic devices and so on.Although great progress has been made in the research of two-dimensional layered semiconductor nanomaterials,there are still great challenges in the controllable preparation of such materials and the fabrication of high-performance devices.First of all,in the preparation of material,at present,a lot of two-dimensional vertical p-n heterostructures are fabricated by the mechanical exfoliation and restacking method,which is suffering by the residual organic impurities,stress,the uncontrollable sample size,morphology,and stack angle,and complicated process.Secondly,in terms of the preparation of high-performance devices,TMDs materials have low optical absorption coefficient and carrier mobility,leading to insufficient performance of photodetectors based on TMDs materials.In this paper,the high quality two-dimensional layered PbI₂/WS₂ vertical heterostructures and Cs₃Bi₂I₉ perovskite nanoplates were prepared through vapor deposition method and solution method respectively.A series of high-performance optoelectronic devices were designed and constructed based on these nanostructures.The innovative research results obtained in this paper can be summarized as follows:1.The high quality PbI₂/WS₂ vertical heterostructures were prepared through vapor deposition method,and the size of heterostructures can reach up to more than 20μm.The growth process is van der Waals epitaxial growth,and the efficient separation and transfer of photo-induced carriers at the heterostructure interface is proved.2.A novel device structure was designed based on the prepared high quality PbI₂/WS₂ vertical heterostructures,which was prepared by means of the electrodes only connecting with the upper PbI₂ layer.Compared with the pure PbI₂ and WS₂ devices fabricated through the same process,the photoresponsivity of the PbI₂/WS₂ vertical heterostructures is improved by 3-4 orders of magnitude.This is due to the photogating effect generated in the device structure,in which the photo-induced electrons are restricted in the lower WS₂ layer and induced a large number of holes in the upper PbI₂layer through capacitive coupling effect.3.The controllable preparation of high quality,lead-free and highly stable Cs₃Bi₂I₉perovskite nanoplates were prepared through a simple and fast liquid phase synthesis method.A new method of PDMS assisted preparation of perovskite optoelectronic device was developed,and a perovskite photodetector with high photoresponsivity and fast response speed was obtained.