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

Molybdenum disulfide (2H-MoS) 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-MoS bulk system are systematically investigated by first-principles calculation to address these issues. We find that the S vacancy V 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 Mo or Mo interstitial Mo also have deep levels that can trap electrons leading to depressed EC. S and S could be the origin of the p-type EC in 2H-MoS, 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-MoS and explain well the experimental observations.