The Research Of Van Der Waals Heterojunction Devices Based On MoS₂ And WSe₂ 2D Semiconductor

The shrinking of transistor's characteristic size promotes the rapid development of semiconductor technology and brings human beings into the information age.However,as the gate length decreases,the gate voltage's ability to control the transistor channel also decreases rapidly.In order to improve the current switching ratio and suppress the short channel effect,the shrinking characteristic size requires that the channel thickness of the transistor also shrinks sharply.Silicon transistors made with the latest Fin-type structure have now reached the 7 nm process node,and its Fin-width?channel thickness?has been reduced to nearly 5 nm.But if the channel thickness of silicon-based transistors continues to be reduced,the ultra-thin silicon film will produce a large number of defects,which will seriously affect the mobility and other electrical properties of silicon transistors.Compared with the traditional silicon semiconductor,two-dimensional?2D?semiconductor have atomically flat surfaces,so they still have stable electrical and optical properties when they reach the limit thickness at the atomic scale.In addition,as the 2D semiconductor transistor itself has the silicon-on-insulator structure,the gate control ability of 2D semiconductor transistor is strong,which can effectively inhibit the short channel effect of the transistor.And 2D semiconductor is expected to solve the main challenges faced by small-scale silicon devices.But the 2D semiconductors have their own advantages and disadvantages so far,and the perfect 2D semiconductor which can replace silicon is still not appeared.Therefore,in order to make full use of the excellent characteristics of existing 2D semiconductors,it is an important direction of2D semiconductor research to combine different 2D semiconductors,learn from each other and realize van der Waals heterojunction devices with special functions.Based on the above research ideas,this paper adopts the method of van der Waals heterointegration to design and prepare 2D semiconductor van der Waals heterojunction devices with different functions,and describes its working mechanism and performance characteristics in detail.The main work is as follows:1.Based on the large pn barrier generated by GaN nanowire and 2D semiconductor MoS₂ vdWs heterojunction,the short-channel MoS₂ transistor with GaN nanowire as the top-gate electrode is prepared.Compared with the traditional top-gate MoS₂ transistor with MOS structure,the van der Waals heterojunction transistor has a quasi-MESFET structure.And the pn barrier in the MoS₂ and the GaN nanowire vdWs heterojunction can be directly used to suppress the generation of gate leakage current.Because there is no insulating gate dielectric in the transistor structure,the control of GaN nanowire top-gate electrode is directly increased,which effectively inhibits the short channel effect of the device.Then this makes the threshold swing?SS?of the short-channel top-gate MoS₂ transistor close to the theoretical limit,and high current switch ratio at room temperature.In addition,physical transfer of GaN nanowire top gate greatly improves the interface quality between top gate and channel.Our work provides a new way to prepare the top gate MoS₂ transistor with excellent performance.2.Because the Fermi energy level of p-type GeSe changes little with the V_g and the Fermi energy level of the bipolar WSe₂ moves widely with the V_g,we fabricate the GeSe/WSe₂ vdWs heterojunction photodetector.And its performance of light detection can be greatly modulated by gate-voltage?V_g?.In addition,we show that the GeSe/MoS₂ vdWs heterojunction has an uncontrollable photovoltaic property,as well as the GeSe/graphene vdWs heterojunction has no photovoltaic property.These proves that the giant V_g tunability of the GeSe/WSe₂ vdWs heterojunction photodetector results from the significantly different sensitivity of the Fermi levels to V_g in the two semiconductor,which further leads to the great change of the Fermi energy level difference(E_fp-E_fn)with V_g.3.Based on the electrical properties of MoS₂ and carbon nanotube thin films,we fabricate the non-volatile MoS₂/CNT hybrid vdWs heterojunction photoinduced memory.In this non-volatile photoinduced memory,V_g is used to control the transfer of photocarriers in the MoS₂/CNT hybrid vdWs heterojunction,as well as their capture and release in charge traps,so as to realize the process of write?store and erase optical signals.The device even can be prepared on a flexible substrate.The vdWs heterojunction photoinduced memory can be prepared on a flexible transparent substrate,and also be used as a light detector.Based on its unique transfer characteristic curve,the device can even be used in the development of ternary CMOS logic circuits.