  Using DFT calculations, we investigate the effects of the type, location, and
density of point defects in monolayer MoS2 on electronic structures and
Schottky barrier heights (SBH) of Au/MoS2 heterojunction. Three types of point
defects in monolayer MoS2, that is, S monovacancy, S divacancy and MoS (Mo
substitution at S site) antisite defects, are considered. The following
findings are revealed: (1) The SBH for the monolayer MoS2 with defects is
universally higher than that for its defect-free counterpart. (2) S divacancy
and MoS antisite defects increase the SBH to a larger extent than S
monovacancy. (3) A defect located in the inner sublayer of MoS2, which is
adjacent to Au substrate, increases the SBH to a larger extent than that in the
outer sublayer of MoS2. (4) An increase in defect density increases the SBH.
These findings indicate a large variation of SBH with the defect type,
location, and concentration. We also compare our results with previously
experimentally measured SBH for Au/MoS2 contact and postulate possible reasons
for the large differences among existing experimental measurements and between
experimental measurements and theoretical predictions. The findings and
insights revealed here may provide practice guidelines for modulation and
optimization of SBH in Au/MoS2 and similar heterojunctions via defect
engineering.
