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

Abstract

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 (238 µA/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 ≥ 9 nm and Td = 4–5 nm, and the optimized non-uniform type-III (GaAs0.1Sb0.9/InAs) TFET is designed with Ts = 8–9 nm and Td = 4–5 nm. The Ioff of non-uniform Tch TFETs can be further suppressed as Td scales down to below 3 nm. However, Ion degradation is observed for non-uniform Tch TFETs with thin Td ≤ 3 nm 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.