Electronic properties of MoS₂/MoO_x interfaces: Implications in Tunnel Field Effect Transistors and Hole Contacts

In an electronic device based on two dimensional (2D) transitional metal dichalcogenides (TMDs), finding a low resistance metal contact is critical in order to achieve the desired performance. However, due to the unusual Fermi level pinning in metal/2D TMD interface, the performance is limited. Here, we investigate the electronic properties of TMDs and transition metal oxide (TMO) interfaces (MoS₂/MoO₃) using density functional theory (DFT). Our results demonstrate that, due to the large work function of MoO₃ and the relative band alignment with MoS₂, together with small energy gap, the MoS₂/MoO₃ interface is a good candidate for a tunnel field effect (TFET)-type device. Moreover, if the interface is not stoichiometric because of the presence of oxygen vacancies in MoO₃, the heterostructure is more suitable for p-type (hole) contacts, exhibiting an Ohmic electrical behavior as experimentally demonstrated for different TMO/TMD interfaces. Our results reveal that the defect state induced by an oxygen vacancy in the MoO₃ aligns with the valance band of MoS₂, showing an insignificant impact on the band gap of the TMD. This result highlights the role of oxygen vacancies in oxides on facilitating appropriate contacts at the MoS₂ and MoO_x (x < 3) interface, which consistently explains the available experimental observations.