Band offsets and stability of WSe${}_2$/RuCl${}_3$ van der Waals charge-transfer contacts

Abstract

The layered Mott insulator $\alpha$-RuCl${}_3$ induces degenerate hole-doping in two-dimensional semiconductors due to its large electron affinity, making it a promising charge-transfer material for establishing ohmic contacts in electronic devices. In order to assess the applicability and guide the design of devices incorporating RuCl${}_3$ it is critical to determine the electronic structure and robustness of the band offsets that underpin the transport properties of semiconductors in contact with RuCl${}_3$. Here, we apply micro-focused angle-resolved photoemission spectroscopy to determine the electronic structure of single-layer WSe${}_2$ contacted to RuCl${}_3$ on hexagonal boron nitride substrates. We find that formation of a functioning WSe${}_2$/RuCl${}_3$ contact leads to a valence band shift of $(0.68\pm 0.05)$ eV towards the Fermi energy in WSe${}_2$. The charge transfer effect is challenging to observe as it depends sensitively on fabrication conditions such as solvent exposure, quality of interface encapsulation and heating of RuCl${}_3$, imposing strict requirements on device design to attain high-quality contacts.

7 pages, 3 figures