Phenomenological Model of Gate-Dependent Kink in I-V Characteristics of MoS₂ Double-Gate FETs

Abstract

A phenomenological model, accounting for interface states at metal-semiconductor contacts, is proposed to explain particular gate-bias-dependent kinking in I-V characteristics sometimes observed in MoS2 FETs. The effect is studied in double-gate FETs by varying top-gate voltage (VTG) and bottom-gate voltage (VBG), with the MoS2 semiconductor layer overlying source/drain (S/D) metal contacts in contact regions. The kink in ID-VTG characteristics is observed for small negative VBG but not for large negative VBG. The model divides the FET into S/D and channel regions, with bias-dependent S/D resistance (RSD) and channel resistance (RCHAN), and with S/D regions having an additional interface state distribution (additional to any interface states associated with semiconductor/dielectric interfaces in the channel region) due to an imperfect metal-semiconductor interface where MoS2 overlies S/D metal. The additional interface states are modeled as a Gaussian distribution of acceptor-like states in the upper region of the semiconductor bandgap. When RSD ≥ RCHAN (VBG less negative), filling of these acceptor-like states as VTG increases creates a kink in ID-VTG characteristics since RSD is a major component of overall resistance limiting drain current, ID. Conversely, when RSD << RCHAN (VBG more negative), filling of these acceptor-like states as VTG increases does not create an ID-VTG kink since RSD is not the major component of resistance limiting ID. The model highlights 1) metal-semiconductor interface states need to be accounted for when modeling MoS2 FETs, and 2) importance of forming metal-semiconductor interfaces with low interface state density to avoid I-V kinks which are detrimental for analog applications.

Keywords

• MoS₂
• double-gate FET
• I-V kink
• interface states
• phenomenological model