Studies On Optoelectronic Properties Of Two Dimensional Semiconductor Heterojunction

Two-dimensional material is the general name of a large class of materials,that is,the form of layered materials reduced to the physical limit of thickness,the most typical representative of which is graphene.The single-atom-thick material was produced by tape-stripping in 2004,and the study of various two-dimensional materials has quickly become a central focus in the field of materials.Unlike traditional three dimensional structural materials,the electron transport during two dimensional materials can be completed in an atomic plane.At the same time,the symmetrical and flat lattice structure enables it to exhibit many unique and superior physical and chemical properties.Nowadays,two-dimensional materials have been widely used in integrated circuits,energy,communication,sensors,biomedicine,aerospace and other fields.However,the application of a single material is often limited by the"short plate effect".For example,the electron mobility of graphene is very high,but the band gap is zero and the switch ratio is low,so it is difficult to be used in logic circuits.The switch ratio of Molybdenum disulfide is larger,but the electron mobility is lower.This led to a gradual shift of emphasis to heterogeneous junctions of different two-dimensional materials.The flat surface of two-dimensional materials and the combination of layers with van der Waals forces that are weaker than chemical bonds result in a easy heterogeneous junctions stacked like building blocks.In this paper,the author bases on common two-dimensional materials such as graphene,molybdenum disulfide and boron nitride,the device structure of heterogeneous junction FET is constructed,and its application in photoelectric detection and storage is mainly studied.The paper is divided into two parts based on device application.The first part is photodetector with planar heterojunction structure of graphene/fullerene.Because of its high carrier mobility,graphene is often used as a component material for high-speed electronic and optoelectronic devices.However,the photoabsorptivity of monolayer graphene is very low.We used fullerenes with uv absorption ability to construct heterojunction to broaden the application range of devices.Firstly,boron nitride was used as the growth template of fullerenes to realize the material growth process with larger grain size.At the same time,a high-performance heterojunction photodetector was realized by using graphene as the channel electrode.The responsivity of the device exceeds 1000 A/W,the response bandwidth is 5 k Hz,and the tunable photoelectric parameters can be realized by changing the potential barrier of the heterogeneous interface,which shows the application value in video imaging and other aspects.The second part is the optoelectronic memory of vertical heterojunction structure of molybdenum sulfide/boron nitride/graphene.Memory and information storage devices are important components of modern digital systems and integrated circuits.Traditional electronic devices based on silicon materials usually face problems of short channels and power consumption when they are gradually reduced in size.Due to the characteristics of atom-level thickness and high heat dissipation coefficient,two-dimensional materials have more advantages in the production of nanoscale transistors with higher integration,and are expected to become the basic building template for the next generation of low-power electronic and photoelectric storage devices.The heterojunction in this chapter was constructed by dry transfer,in which molybdenum sulfide was used as the channel transport layer,boron nitride as the charge tunneling layer,and graphene as the floating gate layer,thus building a kind of memory with flash memory structure.Through both applied voltage and incident light programming,a switching current ratio greater than 10~7,a low static power consumption of about 2 p W,and a faster read/write speed of less than 50 ms can be achieved.In addition,by changing the external excitation conditions,the application value in multi-bit storage is demonstrated.