Residue-free ohmic contacts to transition metal dichalcogenides

Twisted transition metal dichalcogenides (TMDs) have recently demonstrated intriguing phenomena, including the fractional quantum anomalous Hall effect and superconductivity. However, achieving reliable ohmic contacts to TMDs at low temperatures is challenging due to Schottky barriers at the metal-semiconductor interface. One way of making p-type contacts is to use high-work-function metal electrodes, such as platinum; however, the process involved in fabricating these contacts typically introduces contamination to the active layer due to resist residues accumulated during the lithographic process prior to completion of the heterostructure. Here, we present a method for fabricating residue-free ohmic contacts to air sensitive TMD heterostructures by 'flipping' the partially completed heterostructure stack and then depositing metal through a PMMA based stencil mask. This approach avoids resist contamination and preserves a clean van der Waals interface. Using this technique, we fabricated twisted bilayer WSe₂ devices and performed magneto-transport measurements at cryogenic temperatures, and will show data consistent with correlated insulating states at both integer and fractional fillings of moiré superlattices.