Abstract
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 MoOx (x < 3) interface, which consistently explains the available experimental observations.
Highlights
MoOx has a great potential to be used as an efficient hole injection layer by charge transport through the valence band, making a TMD-based p-FET
Given the numerous possible transition metal oxides with a wide range of work functions and electronic structures, and the additional available options to tailor their properties, such as modifying the defect concentration or the cation oxidation states, this research focused on hole contacts based on metal oxides-TMD heterostructures, and opens a new avenue to explore 2D TMDs and TMO interfaces for optimization of the device functionality
Due to the large work function of MoO3, a unique and useful band alignment between MoS2 and MoO3 is observed, which can open a potential application in FET
Summary
Our calculations show that the MoOx interfacial layer can behave as a p-type contact. Our results clarify why the defective MoS2/MoOx interface can be used as an ideal hole contact for TMD-based devices, besides the well-studied organic semiconductors. It behaves as a MoOx hole contact layer, injecting holes into the MoS2.
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