Optoelectronic Effects And Devices Of 2D Bismuth Heterojuctions

Bismuthene as two-dimensional(2D)form of last element in group V,possesses theoretically predicted small band gap and high carrier mobility and induces extensive application prosperity in photodetectors field.However,current bismuth photodetectors confront with challenges of low responsivity or slow response speed out of preparation method or device structure.A strategy to introduce heterojunction interface is proposed here to boost photoelectric properties,so this thesis investigated heterojunctions integration of 2D bismuth with group IV elements and their electrical transportation and photo response parameters with major results as follows:2D Bi/Si heterojunction is characterized by synergistically enhanced(1+1>2)photoelectric effect.Epitaxial 2D Bi on intrinsic Si(111)substrate is featured with high crystallinity,flatness,and uniformity.The heterojunction interface displays photo response under from visible to infrared range:responsivity reaches up to 80 A W^-1,response time is around 3?s,and external quantum efficiency is more than 100%.These parameters are three orders of magnitude better compared with literature results,which can be attributed to the high quality of epitaxial interfaces and photo gain effect induced by trap states at silicon side.As a practical use,2D Bi/Si heterojunction can work as a position-sensitive detector(PSD).The effective working area is 3 mm×3 mm and the nonlinearity is 6.27%under infrared range.To further reduce dark current,graphene/2D Bi heterojunction photodetector has been constructed via mechanical exfoliation and dry transfer process.Compared with 2D Bi/Si heterojunction,graphene/2D Bi has a much lower dark current,thus giving a larger detectivity?10¹¹ Jones with similar response time?48.5?s.Above phenomenon can be explained by the charge transfer between graphene and Bi,thus reducing the Schottky barrier and improving efficiency of carriers'separation.This thesis has experimentally verified the application prospect of 2D Bi heterojunction photodetector and offer theory and experiments basis for construction of heterojunction photodetectors.