Elimination of S Vacancy as the Cause for the n-Type Behavior of MoS2 from the First-Principles Perspective.

Molybdenum disulfide (2H-MoS2) based low-dimensional nanostructure materials have great potential for applications in electronic and optoelectronic devices. However, some of the properties such as the origin of the native n-type electrical conductivity (EC) observed in these materials still remain elusive. Here, the defect properties in the 2H-MoS2 bulk system are systematically investigated by first-principles calculation to address these issues. We find that the S vacancy VS with low formation energy cannot be the origin of n-type EC owing to its deep defect levels within the valence band region. All other donor defects such as antisite MoS or Mo interstitial MoI also have deep levels that can trap electrons leading to depressed EC. SMo and SI could be the origin of the p-type EC in 2H-MoS2, but the concentrations are expected to be rather low due to their high formation energies and can only be enhanced under S-rich/Mo-poor conditions. These results provide the underlying insights on the defect properties 2H-MoS2 and explain well the experimental observations.