Schottky Barrier Study Of Two-dimensional Metal And Semiconductor Edge Contacts

In this paper,2D metallic materials are replaced 3D bulk metals to make contacts with2D semiconductor materials.Therefore,the problem of lattice mismatch between the metal and the two-dimensional semiconductor material is reduced,and the injection efficiency of carriers is improved.In addition,this paper uses edge contact to replace top contact.Thereby,the contact resistance of metal and two-dimensional semiconductor is reduced,and the performance of the device is improved.Based on density functional theory and non-equilibrium Green’s number method,the main research results of this paper are as follows:The effect of different interfacial structures and doping on Schottky barrier of edge contacts based on graphene/Mo S₂was investigated.According to the electron difference density,different interface structures cause different electron distributions,on the contact surface.Since the three structures are formed by edge contact,the tunneling barrier for carriers is very small.By calculating the local projected density of states,it is found that the C–S structure exhibits a smaller p-type Schottky barrier,indicating that it has better transport properties than the other two structures.Next,by doping Mo S2,it was found that the effective doping method can reduce the Schottky-barrier height（SBH）,resulting in smaller contact resistance.Finally,the current magnitudes of different structures are calculated.The current–voltage curves of the undoped and doped C–S structures exhibit rectification and approximately linear characteristics under a small given bias.The tunable of Schottky barrier of planar devices by external electric field and strain is studied.Firstly,four more metallic borophene are used as electrodes to make edge contact with WTe₂.By calculating the density of states,electron differential density and electron distribution maps,it is found that different borophene structures in contact with WTe₂lead to different electronic structures and transport properties.Next by calculating the transmission spectra and local density of states of the four structures,it is found that there is a clear difference in the size of the Schottky barrier.Finally,the effect of the applied electric field on the Schottky barrier is studied.It is found that the external electric field effectively reduces the height of Schottky barrier and induces the ohmic contact between borophene and WTe₂.Secondly,borophene and graphene were used as electrodes for edge contact with black phosphorus.The results show that the small Schottky barrier along zigzag direction of BP is shown in Gra/BP and Boroβ12/BP heterojunctions because of the anisotropy of BP.Next,by applying an external electric field,it is found that the electric field not only can modulate the height of the Schottky barrier effectively but also the type of Schottky contact.Finally,the effect of strain on the Schottky barrier of the heterojunction is investigated.The result show that the applied strain can modulate both the electron barrier and the hole barrier for armchair BP based heterojunction.Sub-ten-nanometer Schottky barrier field effect transistors are studied.Firstly,using WSSe as channel material,we investigate the performance of the in-plane（IP）Sn and Ti contacted sub-10 nm（gate length=5.1,6.1,7.3,8.8 nm）single-gated（SG）monolayer（ML）Juanus WSSe Schottky barrier field-effect transistors（SBFETs）.The transfer characteristics,total gate capacitance,intrinsic delay time and dynamic power indicator are studied.The results show that the the on-state current of the Sn contacted 5.1 nm WSSe SBFETs reaches up to 1104.2μA/μm,which is far beyond the requirements of the International Technology Roadmap for Semiconductor（ITRS）high performance（HP）application targets.Secondly,using black phosphorus（BP）as channel material,we investigate the performance of the in-plane（IP）graphene and boropheneβ₁₂contacted sub-10 nm（gate length=5.1,6.1,7.3,8.8nm）single-gated（SG）and double-gated（DG）monolayer（ML）BP Schottky barrier field-effect transistors（SBFETs）.The results show that the calculated on-state currents of the IP graphene contacted sub-10 nm SG ML BP SBFETs are 1064.8,1272.3,1676.5,1363.8μA/μm,which are far beyond the requirements of the IRTS HP application targets.Compared with graphene electrode,the on-state currents of IP boropheneβ12 contacted 5.1-8.8 nm SG ML BP SBFETs can only satisfy about 10%–70%requirement of HP standards because of the strong metal induced gap states（MIGS）in the channel.Moreover,we further investigated the effect of DG model on the device performance.The results indicated that the gate electrostatic control is significantly improved by using DG model.The on-state currents of IP graphene and boropheneβ12 contacted 5.1-8.8 nm DG ML BP SBFETs are increased by a factor of1.37–1.56 and 1.16–3.59 compared with SG model.As a result,the large on-state currents of IP configurations based on graphene/ML BP/graphene can greatly stimulate the potential of BP transistors.