Theoretical and experimental investigation of vacancy-based doping of monolayer MoS$_2$ on oxide

TL;DR

This study combines theoretical simulations and experimental methods to investigate how vacancies in oxides and MoS$_2$ layers influence the electronic properties of monolayer MoS$_2$, revealing vacancy-induced doping effects relevant for device applications.

Contribution

It provides a comprehensive analysis of vacancy effects on MoS$_2$-oxide interfaces through density-functional simulations and experimental validation, highlighting vacancy-induced doping mechanisms.

Findings

Oxygen vacancies induce metallic behavior in MoS$_2$-oxide systems.

Vacancy-induced doping enables n-type conduction in monolayer MoS$_2$.

Experimental evidence confirms vacancy-related doping effects in fabricated transistors.

Abstract

Monolayer transition metal dichalcogenides are novel, gapped two-dimensional materials. Toward device applications, we consider MoS$_2$ layers on dielectrics, in particular in this work, the effect of vacancies on the electronic structure. In density-functional based simulations, we consider the effects of near-interface O vacancies in the oxide slab, and Mo or S vacancies in the MoS$_2$ 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 MoS$_2$-dielectrics system and for isolated dielectric layers for reference. Among our results, we find that with O vacancies, both the Hf-terminated HfO$_2$-MoS$_2$ system, and the O-terminated and H-passivated Al$_2$O$_3$-MoS$_2$ systems appear metallic due to doping of the oxide slab followed by electron transfer into the MoS$_2$, in manner analogous to modulation doping. The n-type doping of monolayer MoS$_2$ by high-k oxides with oxygen vacancies then is experimentally demonstrated by electrically and spectroscopically characterizing back-gated monolayer MoS$_2$ field effect transistors encapsulated by oxygen deficient alumina and hafnia.