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

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 MoS
₂
FETs. The effect is studied in double-gate FETs by varying top-gate voltage (V
_TG
) and bottom-gate voltage (V
_BG
), with the MoS
₂
semiconductor layer overlying source/drain (S/D) metal contacts in contact regions. The kink in I
_D
-V
_TG
characteristics is observed for small negative V
_BG
but not for large negative V
_BG
. The model divides the FET into S/D and channel regions, with bias-dependent S/D resistance (R
_SD
) and channel resistance (R
_CHAN
), 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 MoS
₂
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 R
_SD
≥ R
_CHAN
(V
_BG
less negative), filling of these acceptor-like states as V
_TG
increases creates a kink in I
_D
-V
_TG
characteristics since R
_SD
is a major component of overall resistance limiting drain current, I
_D
. Conversely, when R
_SD
<< R
_CHAN
(V
_BG
more negative), filling of these acceptor-like states as V
_TG
increases does not create an I
_D
-V
_TG
kink since R
_SD
is not the major component of resistance limiting I
_D
. The model highlights 1) metal-semiconductor interface states need to be accounted for when modeling MoS
₂
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.