Optimization of III-V heterojunction tunnel FET with non-uniform channel thickness for performance enhancement and ambipolar leakage suppression

The optimized non-uniform channel thickness design for type-II and -III GaAs1-xSbx/In1-yGayAs heterojunction tunnel FETs (TFETs) is proposed for improving on currents (Ion) and suppressing ambipolar leakage. Quantum confinement induced bandgap widening as a function of channel thickness (Tch) is considered. For non-uniform Tch TFETs, the thick source/channel junction thickness (Ts) with small bandgap maintains small tunneling barrier and high Ion, while the thin drain/channel junction thickness (Td) with large bandgap reduces the ambipolar leakage. With the same Ioff, type-II non-uniform TFET exhibits 4 times higher Ion (238μA/μm) than the type-II uniform TFET, and type-III non-uniform TFET shows 63% improvement in Ion (538 μA/μm) compared with the type-III uniform TFET. The optimized non-uniform type-II TFET (GaAs0.4Sb0.6/In0.65Ga0.35As) is designed with Ts ≥ 9nm and Td = 4-5nm, and the optimized non-uniform type-III (GaAs0.1Sb0.9/InAs) TFET is designed with Ts = 8-9nm and Td = 4-5nm. The Ioff of non-uniform Tch TFETs can be further suppressed as Td scales down to below 3nm. However, Iondegradation is observed for non-uniform Tch TFETs with thin Td≤ 3nm due to extra energy barrier. The Ioff of type-III non-uniform TFETs can be further reduced by using gate-to-drain underlap design. Compared with the conventional TFETs with uniform Tch, the non-uniform Tch TFETs exhibit significant improvement in subthreshold swing, which benefits ultra-low power applications. © 2018 The Japan Society of Applied Physics.