Fabrication and characterization of graphene-based heterostructure using molybdenum as alternative electrodes

Abstract

Interlayer coupling in graphene heterostructures can be used to modify their charge transport properties for the use in nanoelectronics applications. To achieve high-performance devices, graphene is typically encapsulated by two thin sheets of hexagonal boron nitride (hBN) and contacted using Cr/Au as electrodes. ​ In this research, Mo was selected as alternative stand-alone electrodes to simplify the fabrication process. We have developed a recipe for the fabrication of field-effect transistor (FET) using twisted bilayer graphene (tBLG) as a transport channel. Mo was employed to make one-dimensional (1D) contacts to the edges of graphene by sputtering. Electronic transport measurement was then performed on the FET devices to investigate the quality of Mo contacts. We achieved ohmic contacts between Mo and graphene. The contact resistivity between Mo and graphene reached a maximum value of around 1,300 Ω⋅µm at charge neutrality point and decreased to 975 Ω⋅µm at a carrier density of ~4×1012 cm-2. However, we have observed that the contact resistivity increases over time likely due to the oxidization of Mo. Despite the increase in contact resistivity, the Mo contacts still exhibit ohmic behavior after 3 months and it can be used to investigate transport phenomena in graphene. In this study, the room-temperature electron and hole mobilities of tBLG reached values as high as 27,000 and 21,000 cm2/V⋅s indicating that Mo electrodes do not hinder the transport characteristics of graphene.