Performance Improvement And Investigation Of Tunneling Field-effect Transistor

With the rapid development of integrated circuit?IC?industrialization,the power consumption problem in VLSI is the inevitable problem which restricts its advance.Reducing device supply voltage(V_DD)is the most effective approach to decrease the IC's power consumption.When V_DD is further reduced,the conventional metal-oxide-semiconductor Field-Effect Transistor?MOSFET?cannot keep on the enhancement of performance,and static power consumption increases dramatically due to leakage current shows exponential increasing.The tunneling field effect transistor?TFET?based on band-to-band tunneling?BTBT?mechanism is one of the most promising candidate to realize ultralow power dissipation,due to its excellent switching characteristics at a very low supply voltage such as 0.3 V and the good compatibility with the current MOSFET platform.A key challenge of TFETs is maintaining sufficient high ON-state current I_ONN and steep SS simultaneously which may hinder its widespread application.Novel band structure designs and high mobility materials are the most effective means to solve that.GeSn alloys with quasi direct bandgap and high hole mobility,can generate a decent BTBT current and are promising with pTFETs compared with other materials.And TFET structures with type-II staggered tunneling junction have been widely used to improve the BTBT probability and I_ONN due to its smaller effective bandgap.To improve I_ON and SS,GeSn and GaAsN/GaAsBi type-II TFETs were investigated in this thesis work.The main contents and results are illustrated as follows.The physical properties of GeSn film and electrical properties of GeSn MOSFETs and GeSn TFETs were investigated.The results of transmission electron microscope?TEM?,atomic force microscope?AFM?and high resolution X-Ray diffraction?HR-XRD?depict the defect free GeSn/Si interface and the high crystallinity of 4-nm GeSn films on Si?001?and?111?.GeSn QW pMOSFETs on Si?111?demonstrate a high effective hole mobility of 505 cm²/Vs,and the effective hole mobility of GeSn?111?pMOSFETs had an improvement of 40%compared with GeSn?001?devices.?111?-oriented GeSn pTFET achieves a steep SS of 56mV/decade and a high ON-state/OFF-state current ratio of 10⁷,which are superior to those of the other reported non-Si pTFETs with a small bandgap.We speculate that the superior crystalline of GeSn channel and the higher quality of high-?/channel interface for the device on?111?would lead to an improved G_BTBT and I_ON in?111?-oriented TFET compared to the device on?001?.Additionally,GeSn channel on?111?has much higher?_eff than?001?channel,which reduces the channel resistance and enhances I_ON in TFET on?111?.Theoretical investigation of GaAsBi/GaAsN TFETs with type-II staggered tunneling junction was carried out.Strain-symmetrized GaAs_0.85Bi_0.15/GaAs_0.92N_0.08 staggered hetero-nTFET achieves 7.8 and 550 times higher I_ON compared to InAs and In_0.53Ga_0.47As homo-TFETs,respectively,at the supply voltage of 0.3 V.The effect of material composition,the t_body,N_a and N_v in source region on the device performance was characterized with the analytical model.T?E?and the drive current of the devices can be significantly boosted by increasing Bi and N compositions,reducing the t_body,and optimizing the N_a in source region.