Reexamination of the Schottky Barrier Heights in Monolayer MoS2 Field-Effect Transistors

Owing to its promising electronic application of monolayer (ML) MoS2, ML MoS2-metal contacts have been widely explored. The experiments reveal a very strong Fermi level pinning, and the corresponding pinning factor is about 0.1 [Nature 2018, 5.57, 696-700], but all the existing calculations give a larger pinning factor of about 0.3. Such an apparent discrepancy is attributed to the defects in samples. In this paper, the Schottky barriers are reexamined in the pristine ML MoS2 field-effect transistors (FETs) with a series of metal electrodes (Au, Pt, Ag, Ti, Cr, Pd, Ni, and ML CCr2) by using ab initio quantum transport simulation. The Schottky barrier heights obtained from our ab initio quantum transport simulation are in better agreement with those observed in experiments for Au and Pt electrodes, and the calculated pinning factor is also improved. Our work highlights the importance of the inclusion of the coupling between the electrode and channel in determining the pinning behavior. Hence, ab initio quantum transport simulation is an improved method to determine the SBH and the pinning factor in low-dimensional semiconductor FETs.