Direct access to the graphene–metal interface using Raman spectroscopy to study the origin of contact resistance in operational devices

Abstract

We present and validate a reliable approach for investigating the graphene–metal interface in the top metallic contacts of operational devices using Raman spectroscopy. A transparent substrate was optimized for graphene visualization and processing by adjusting the thickness of aluminum and amorphous silicon nitride on a glass substrate. After graphene photolithography and Cr/Au contact fabrication, the device was flipped upside down to directly expose the graphene–metal interface for Raman analysis using 457 nm excitation. Electrical characterization was performed on the same devices: the sheet resistance was measured using the van der Pauw method, and the contact resistance was determined using the transfer length method. This approach enables direct correlation between Raman features—an increased D peak and a reduced 2D peak at the graphene–metal interface—and electrical parameters of the contact. In particular, the higher sheet resistance of graphene beneath the metal corresponds to the reduced p-doping obtained using Raman spectroscopy.