Decreased n-type behavior of monolayer MoS2 crystals annealed in sulfur atmosphere

Herein, we report decreased n-type behavior of mechanically exfoliated monolayer MoS₂ crystals via annealing in sulfur atmosphere. The Raman, photoluminescence, and X-ray photoelectron spectroscopy (XPS) measurements consistently suggested decreased n-type behavior of the monolayer MoS₂ crystals after an hour of thermal annealing at 200 °C in sulfur atmosphere. Such decreased n-type behavior could be attributed to the reduced concentration of sulfur vacancies after the annealing, suggested by the analysis of XPS spectra. Furthermore, after the annealing in sulfur atmosphere, the monolayer MoS₂ transistors exhibited positively shifted threshold voltages and reduced on-currents, confirming decreased n-type conduction. These results demonstrate that the reduction of the concentration of sulfur vacancies decreases n-type behavior in monolayer MoS₂, providing valuable information on understanding the effect of sulfur vacancies on the performance of monolayer MoS₂ devices.