Ab Initio Computer Simulations on Interfacial Properties of Single-Layer MoS₂and Au Contacts for Two-Dimensional Nanodevices

The functionality and performance of devices based on atomically thin two-dimensional (2D) materials strongly depend on the quality of the employed 2D material. Although molybdenum disulfide (MoS2) is an excellent candidate for future applications in nanoelectronics, MoS2 films have not yet reached the level of purity achieved in silicon technologies. At present, the formation of small and extended defects in the material is inevitable during the growth process, and this has a non-negligible impact on the electronic properties of MoS2. Furthermore, defects are also thought to affect nontrivially the resistance at the MoS2-metal contact and the injection of carriers. In this work, we systematically and thoroughly assess the impact of some of the most commonly occurring defects in MoS2 (such as vacancies, substitutions, and grain boundaries) not only from the point of view of the material's properties but also by looking at MoS2-metal contacts. To do so, we carry out ab initio computer simulations in the density functional theory (DFT) framework coupled with surface simulations based on the Green's function formalism. Our simulation approach allows us to obtain more realistic models of MoS2 interfaces with Au. Moreover, this is the first theoretical study in which the effect of grain boundaries on the MoS2-Au contact properties is explored. Results suggest that S vacancies have a detrimental impact on the quality of the metal contacts, whereas Mo vacancies strongly improve the electron injection from the metal to MoS2. Antisite Mo defects also increase the electron injection rate by acting as "conductive bridges"between the Au electrode and the 2D material. Finally, each of the grain boundaries considered here improves the quality of the contact. We expect our study to provide the necessary theoretical foundation for the design of MoS2-metal contacts with suitable characteristics.