Charge Transport Regimes of MoS2 Nanosheets at Cryogenic Temperatures : Implications for Cryogenic Electronics

The electron transport of n-type back-gated MoS2 field-effect transistors is investigated in the temperature range of 0.3–271 K. The electrical characteristics exhibit significant variations in the drain current in the subthreshold region, when the drain voltage is sufficiently low. The data analysis reveals two distinct charge transport mechanisms at high temperatures. At high gate voltages, charge transport is well described by variable range hopping theory, which suggests the Efros–Shklovskii regime, while at low gate voltages, we observe a transition to the conventional thermal activation regime. The observed phenomena are at considerably greater device dimensions compared to previously reported, as going to sub-Kelvin regimes loosens the dimensional restraints on the device. Moreover, a huge temperature-dependent threshold voltage shift (δVTH/δT) is observed in the whole temperature range, approximately 110 mV/K, incredibly spanning as much as 30 V, with VTH increasingly more positive with decreasing temperature. Evidence of a resistive network for charge carriers is also seen, as there appeared to be parallel channels of conduction within the FETs, each with a different threshold voltage. All this physics needs to be factored in should 2D material FETs be considered for quantum electronics at cryogenic temperatures.