Multi-Field Modulations In Van Der Waals Layered Photodetectors

Van der Waals layered materials have been potential candidates of optoelectronic devices due to excellent electronic and optical properties,such as wide band gap distribution range,strong light absorption,and high carrier mobility.So far,highperformance room temperature infrared photodetectors,high polarization-sensitive photodetectors,and high-performance solar cells based on Van der Waals layered materials have been reported.However,there are still some basic scientific issues that need to be further studied in depth,such as defects effect in Van der Waals layered materials,interface between Van der Waals layered material and metal,and interface of Van der Waals heterostructure.This paper delves into the material growth,device preparation,working mechanism,and potential application of Van der Waals layered photodetectors.Particularly,this paper systematically studies the preparation method of layered GeSe,the mechanism of defects-induced extrinsic photoconduction effect in GeSe and GeS,the working mechanism of InSe photodetector modulated by back-toback Schottky electric field,and the working mechanism of GeSe/InSe/Cr heterostructure modulated by both GeSe/InSe bulit-in electric field and InSe/Cr Schottky electric field.This work provides the theoretical and experimental support for high-performance room temperature photodetectors.The main content of this paper is as follows:1.The study of the preparation method of layered GeSe.High-quality GeSe single crystals are obtained through chemical vapor transport method and the lattice quality and chemical composition are fully characterized.The anisotropic absorption property is confirmed by first-principles theory and the polarization-resolved visible and near infrared micro-area scanning photocurrent mapping technique is established.A polarization-sensitive GeSe photodetector with high dichroic ratio(2.16 at 830 nm)is fabricated.Furthermore,the influences of defect states on transport characteristics,power density dependent photocurrent,and response speed are investigated.The carrier transport mainly manifests as thermally excited transport at high temperatures and hopping transport at low temperatures,respectively.Shallow trap defects contributed to the nonlinear relation between photocurrent and power density.2.The study on the mechanism of GeSe and GeS photoconductive devices modulated by defect localized field.The defect types that may generated during the growth of GeSe and GeS and their formation energy are investigated by the first-principles theory.Then,the influences of different defects on the electronic structure and photoelectric properties of GeSe and GeS are further studied.It is found that Ge vacancies,the most easily formed defects in Group ?-? Van der Waals layered materials,will p-dope materials and expand their detection band.The existence of Ge vacancies in GeSe grown by chemical vapor transport method is experimentally verified through STEM.And the detection waveband of GeSe and GeS photoconductive detectors are expanded from 1000 nm and 780 nm to 1.6 ?m and 1.55 ?m,respectively.3.The study on mechanism of InSe photodetector modulated by back-to-back Schottky electric field.The abnormal rectification characteristics of the symmetrical Cr-InSe-Cr photodiode are observed.Through finite element analysis,it is found that the abnormal characteristics are caused by the uneven contact area of InSe/Cr interface and the influence of the interface charge on the potential barrier.Obvious photovoltaic effect is observed in InSe photodiode with asymmetric Schottky barriers.As the barrier difference increases,the open-circuit voltage and short circuit current increase.Furthermore,the characteristics of Cr/InSe/Cr photodiode under point-irradiation are studied,and the applications of logic devices based on photoelectric joint regulation are demonstrated.4.The study on mechanism of GeSe/InSe/Cr Van der Waals heterostructure modulated by bulit-in electric field and Schottky electric field.GeSe/InSe/Cr Van der Waals heterostructure exhibits reverse rectification characteristics and shows an extremely low forward current.The potential distributions of GeSe/InSe/Cr heterojunction are measured by Kelvin probe force microscopy technology.And the electric characteristics of heterojunction is explained well by above potential distribution results.This paper also studies the optoelectronic characteristics of GeSe/InSe/Cr heterostructure.The device exhibits a high light on/off ratio,high responsivity,and fast response speed.