Intrinsic disorder effects on device performance of few-layer MoS₂ field-effect transistors

Field-effect transistors (FETs) made by two dimensional (2D) materials attract attention because of high on-off ratios and negligible short-channel effects. The 2D material of MoS₂ has been studied for years while problems from contact, interface, and structural disorders have not been solved. There are a lot of reports to give a wide range of electron mobility and the best performance of a single-layer MoS2 FET is still in debate. We present a large variation of disorders in MoS2 flakes exfoliated from the same bulk. The disorder dominate the low performance of FETs. In particular, for high performance devices, the mobility increases with decreasing temperature and the device reveals metallic behaviors. Setting the FET in an on state, the conductivity of high-performance devices is close to e2/h, giving a standard to check the quality. There are some disorders resulting in a large decrease in conductance as well as in the FET mobility. On the other hand, the subthreshold swings are independent from the mobility. The disorder effects dominate to low performance thus growth of perfect 2D crystals is essential for the application of 2D FETs.