Doping plays a key role in modulating electronic properties of 2D semiconductors, and thus is vitally important for next-generation nanoelectronics and optoelectronics devices. However, how to effectively tune the dopant ionization energy (IE) so as to achieve robust and controllable $n$-type or $p$-type conductivities in 2D semiconductors is still a significant challenge. Here, using first-principles calculations, we demonstrate an effective IE-tuning route for 2D semiconductors using dielectric substrates. Taking ${\mathrm{X}}_{\mathrm{S}}$ (X = Cl, Br, I) in ${\mathrm{MoS}}_2$ as examples, we show that the dielectric substrate is able to tune deep dopants to shallow ones, and the dopant IE depends on which S layer the dopant is located in. Specifically, the IE of ${\mathrm{I}}_{\mathrm{S}}$ is reduced from 0.63 eV for the freestanding ${\mathrm{MoS}}_2$, to 0.39 eV when ${\mathrm{MoS}}_2$ is on a ${\mathrm{SiO}}_2$ substrate, further to 0.17 eV when ${\mathrm{MoS}}_2$ is on an ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrate, and the IEs of ${\mathrm{I}}_{\mathrm{S}}$ in the inner and outer S layers differ by 0.22 eV with an ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrate. Correspondingly, the carrier concentrations can be tuned by selecting different substrates or doping layers. We reveal that the remarkable IE reduction is originated from the electronic and ionic screenings of the substrate. Our results not only shed light on the substrate screening effects on the dopant properties, but also suggest a practical route to achieve controllable $n$-type or $p$-type carrier concentrations for 2D semiconductors.

• Received 25 September 2016

DOI:https://doi.org/10.1103/PhysRevB.95.165447