Study of fully-depleted Ge double-gate n-type Tunneling Field-Effect Transistors for improvement in on-state current and sub-threshold swing

Highlights: • A novel fully-depleted (FD) Ge double-gate (DG) Tunneling Field-Effect Transistors (TFET) structure is proposed. I_on=3.96×10^-5 A/μm is achieved. • The fully-depleted device structure enhances I_on and on-off ratio about 1 order of magnitude comparing with the Normal Ge DG-TFET. • The impact of the workfuntion of metal gate Φ_m and the doping concentration of n+-type-channel N_D is investigated. • To reduce I_off and improve the device performance, FD Ge DG-TFET with various L_D is investigated. • With optimized device parameters, sub-threshold swing SS=25.5mV/decade and on-off ratio I_on/I_off=1.58×10⁷ are achieved. In this paper, a fully-depleted (FD) Ge double-gate (DG) n-type Tunneling Field-Effect Transistors (TFET) structure is studied in detail by two-dimensional numerical simulation. The simulation results indicated that the on-state current I_on and on-off ratio of the FD Ge DG-TFET increases about 1 order of magnitude comparing with the Conventional Ge DG-TFET, and I_on=3.95×10^-5 A/μm and the below 60 mV/decade subthreshold swing S=26.4 mV/decade are achieved with the length of gate L_D=20 nm, the workfuntion of metal gate Φ_m=0.2 eV and the doping concentration of n⁺-type-channel N_D=1×10¹⁸ cm^-3. Moreover, the impacts of Φ_m, N_D and L_D are investigated. The simulation results indicated that the off-state current I_off includes the tunneling current at the middle of channel I_B the gated-induced drain leakage (GIDL) current I_GIDL. With optimized Φ_m and N_D, I_off is reduced about 2 orders of magnitude to 2.5×10^-13 A/μm with L_D increasing from 40 nm to 100 nm, and on-off ratio is increased to 1.58×10⁷.