Electrical Doping Effect of Vacancies on Monolayer MoS₂

Doping of transition-metal dichalcogenides (TMDCs) is an effective way to tune the Fermi level to facilitate the band engineering required for different types of devices. For TMDCs, a controversy abounds with regard to the doping role played by vacancy-type defects. Here, we report a detailed study based on first-principles calculations proposing that the native sulfur vacancies (V_S) can significantly alter the electrical doping level in MoS₂ and tune the material to exhibit conventional n- or p-type semiconductor characteristics. In particular, we reveal that the lower concentration of the single V_S (2.8 and 6.3%) yields p-type characteristics, whereas the higher concentration of the single V_S or a cluster of V_S (12.5, 18.8, and 25.0%) yields n-type characteristics. The trend is consistent with previous X-ray photoelectron spectroscopy and scanning tunneling microscopy results. Employing this method of tuning the electron doping level, we modeled a commonly used metal–semiconductor interface to demonstrate both n- and p-type Schottky contact behaviors. Interestingly, we found that the defect configuration could also tune the doping and hence the contact. Simulation of the electric current at the interface as a function of the bias voltage provides a reference for how the electrical characteristics would shift on the basis of the change in vacancy concentration. Our study reveals that the V_S of monolayer MoS₂ at the MoS₂–metal interface play an important role in determining its electrical behavior and suggests that developing methods to control or engineer such defects for controlling the electron doping level could be a viable alternative to conventional doping with foreign atoms.