Multi-scale Simulation Of Physical Properties And Device Characteristics Of Hexagonal SiVA And Orthogonal CVA Two-dimensional Materials

The miniaturization of field-effect transistors(FETs)in integrated circuits can greatly improve performance and reduce costs.With the arrival of the sub-10 nm technology node,compared with traditional silicon as the channel material of the limit size FET,two-dimensional(2D)semiconductor channel materials have many advantages: Atomically thin thickness improves electrostatic control ability of gate;The smooth surface without dangling bonds can reduce the trap state scattering and surface roughness to improve the ability of carrier transport.However,zero-bandgap graphene cannot achieve the switching behavior of transistors;The molybdenum disulfide transistors are difficult to apply to high-performance devices due to the impediment of low on-state current;Black phosphorus and indium selenide have poor stability with degraded device performance in the air.Therefore,finding suitable transistor channel materials remains a great challenge.The interface contact of 2D materials is also an important factor that affects or even governs device performance.Due to the lack of stable and efficient doping technology,2D materials are often in direct contact with metals for carrier injection.Schottky barrier(SB)frequently exists in 2D semiconductor-metal contacts,thereby affecting the performance of 2D FETs.Low SB or Ohmic Contacts are the best choice for realizing the intrinsic properties of 2D channel materials.Based on first-principles calculations and the non-equilibrium Green’s function(NEGF)method,this thesis has finished a series of multi-scale simulation studies from exploring the electronic properties of new 2D materials and their transistor device characteristics to the contact characteristics of the semiconductor-metal interface of devices:(1)The stability,electronic properties of the 2D Si VA(VA = N,P,As,Sb,Bi)semiconductor materials with a hexagonal honeycomb structure,and transport characteristics in atomic-scale MOSFET devices.The phonon spectrum verifies the dynamic stability of 2D Si VA.The calculation of electronic band structure shows that the bandgap of 2D Si VA ranges from 0.91 to 1.65 e V,which is suitable as the channel material of FET.The IV curves of devices obtained by the NEGF method show that 2D Si P has the best device performance as a FET channel material.The on-state current of a 2D Si P n MOSFET with a gate length of 10 nm can reach 1292 μA/μm,which can meet 72% of the high-performance requirement of IRDS 2020.Therefore,2D Si P has the potential as a new generation MOSFET channel material.(2)The stability,electronic properties of orthogonal 2D CVA(VA = P,As,Sb,Bi)semiconductor material,and transport characteristics in atomic-scale TFET devices.The phonon spectrum verifies the dynamic stability of 2D CVA.The band gap ranges of 2D CVA are 0.29 ～ 0.75 e V,which are suitable for TFET channel materials.2D CVA have obvious electronic anisotropy,including anisotropic band structure,carrier effective mass,carrier mobility,and anisotropic device performance.The on-state current of 2D CAs p TFET is 2616μA/μm,which can satisfy 146% of the IRDS 2020 standard for high performance.Hence,it has outstanding performance in high-performance TFET device applications.(3)Interfacial characteristics of Graphene(Gr)/CVA(VA = P,As,Sb,Bi)vertical van der Waals heterostructure.The most stable structures are determined by calculating the total energy of the stacked configurations,the curves of the binding energy-distance between the heterostructure interface.The electronic band structures show that the Gr/CP and Gr/CAs heterostructures have Schottky barrier heights(SBH)of 0.01 e V and 0.43 e V,respectively,while the Gr/CSb and Gr/CBi heterostructures are Ohmic contacts.As the atomic numbers of VA increase,the Gr/CVA heterostructures exhibit different work functions,electron flow directions,charge distributions,and electric dipole moments,and the probability of interface tunneling gradually increase.