Schottky Barrier Variable Graphene/Multilayer-MoS₂ Heterojunction Transistor Used to Overcome Short Channel Effects

Abstract

A single-layer MoS 2 achieves excellent gate controllability within the nanoscale channel length of a field-effect transistor (FET) owing to an ultra-short screening length. However, multilayer MoS 2 (ML-MoS 2 ) is more vulnerable to short channel effects (SCEs) owing to its thickness and long screening length. We eliminated the SCEs in an ML-MoS 2 FET (thickness of 4–13 nm) at a channel length of sub-30 nm using a Schottky barrier (SB) variable graphene/ML-MoS 2 heterojunction. Although the band modulation in the ML-MoS 2 channel worsens with a decrease in the channel length, which is similar to the SCEs occurring in conventional FETs, the variable Fermi level ( E F ) of a graphene electrode along the gate voltage allows control of the SB at the graphene/MoS 2 junction and backs up the current modulation through a variable SB. Electrical measurements and a theoretical band simulation demonstrate the efficient SB modulation of our graphene nanogap (GrNG) ML-MoS 2 FET with three distinct carrier transports along V gs: a thermionic emission at a low SB, Fowler–Nordheim tunneling at a moderate SB, and direct tunneling at a high SB. Our GrNG FET shows an extremely high on–off current ratio of ∼10 8, which is approximately three-orders of magnitude better than a previously reported metal nanogap (MeNG) FET and a self-aligned metal/graphene nanogap FET with a similar MoS 2 thickness. Our GrNG FET also exhibits a 100,000-times higher on–off ratio, 100-times lower subthreshold swing, and 10-times lower drain induced barrier.