N-type and p-type molecular doping on monolayer MoS 2 .

Monolayer MoS 2 has attracted much attention due to its high on/off current ratio, transparency, and suitability for optoelectronic devices. Surface doping by molecular adsorption has proven to be an effective method to facilitate the usage of MoS 2 . However, there are no works available to systematically clarify the effects of the adsorption of F 4 TCNQ, PTCDA, and tetracene on the electronic and optical properties of the material. Therefore, this work elucidated the problem by using density functional theory calculations. We found that the adsorption of F 4 TCNQ and PTCDA turns MoS 2 into a p-type semiconductor, while the tetracene converts MoS 2 into an n-type semiconductor. The occurrence of a new energy level in the conduction band for F 4 TCNQ and PTCDA and the valence band for tetracene reduces the bandgap of the monolayer MoS 2 . Besides, the MoS 2 /F 4 TCNQ and MoS 2 /PTCDA systems exhibit an auxiliary optical peak at the long wavelengths of 950 and 850 nm, respectively. Contrastingly, the MoS 2 /tetracene modifies the optical spectrum of the monolayer MoS 2 only in the ultraviolet region. The findings are in good agreement with the experiments.