Theoretical and experimental investigation of vacancy-based doping of monolayer MoS₂ on oxide

Monolayer (ML) transition metal dichalcogenides are novel, gapped two-dimensional materials with unique electrical and optical properties. Toward device applications, we consider MoS₂ layers on dielectrics, in particular in this work, the effect of vacancies on the electronic structure. In densityfunctional based simulations, we consider the effects of near-interfaceOvacancies in the oxide slab, andMoor S vacancies in the MoS₂ layer. Band structures and atom-projected densities of states for each system and with differing oxide terminations were calculated, as well as those for the defect-free MoS₂-dielectrics system and for isolated dielectric layers for reference. Among our results, we find that with O vacancies, both the Hf-terminated HfO₂-MoS₂ system, and the O-terminated and H-passivated Al₂O₃-MoS₂ systems appear metallic due to doping of the oxide slab followed by electron transfer into the MoS₂, in manner analogous to modulation doping. The n-type doping of MLMoS₂ by high-k oxides with oxygen vacancies then is experimentally demonstrated by electrically and spectroscopically characterizing back-gated MLMoS₂ field effect transistors encapsulated by oxygen deficient alumina and hafnia.