Low-temperature behaviors of multilayer MoS2 transistors with ohmic and Schottky contacts

We report the low-temperature characterization of back-gated multilayer molybdenum disulfide (MoS2) thin-film transistors (TFTs) based on mechanically exfoliated natural MoS2 crystals. Although all the tested MoS2 TFTs are fabricated with the same processes and materials, the current-voltage characteristics of MoS2 TFTs between 77 K and 300 K indicate the existence of two distinct transport behaviors in MoS2 TFTs. One group with a negligible Schottky barrier shows temperature-independent large field-effect mobility, whereas the other group with a high Schottky barrier exhibits significantly lower mobility with a large dependence on temperature variation. We have revealed that the temperature dependence originates from the different carrier injection mechanisms at the source-channel junction, where the intrinsic variation of electronic properties of natural MoS2 crystals can strongly influence the Schottky barrier. Given that sample-to-sample variations are commonly observed in MoS2 TFTs, the metal-semiconductor junction of the as-fabricated device is of paramount importance, and so the low-temperature measurement of current-voltage characteristics of a multilayer MoS2 transistor can be a practical means to investigate the contact properties of natural MoS2 TFTs. Our comprehensive study advances the fundamental knowledge of the transport mechanisms particularly through the metal-MoS2 interface, which will be a critical step toward high-performance electronics based on 2D semiconductors.