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 (Vs) 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 Vs 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 Vs 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.