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.