Electron transport and the effect of current annealing in a two-point contacted hBN/graphene/hBN heterostructure device

Abstract

In this work, we fabricated a 2D van der Waals heterostructure device in an inert nitrogen atmosphere by means of a dry transfer technique in order to obtain a clean and largely impurity free stack of hexagonal boron nitride (hBN)-encapsulated few-layer graphene. The heterostructure was contacted from the top with gold leads on two sides, and the device's properties including intrinsic charge carrier density, mobility, and contact resistance were studied as a function of temperature from 4K to 270K. We show that the contact resistance of the device mainly originates from the metal/graphene interface, which contributes a significant part to the total resistance. We demonstrate that current annealing affects the graphene/metal interface significantly, whereas the intrinsic carrier density and carrier mobility of the hBN-encapsulated few-layer graphene are almost unaffected, contrary to often reported mobility improvements. However, after current annealing, a 75% reduction in the contact resistance improves the overall performance of such a heterostructure device and the backgate-dependent transfer curve becomes more symmetric with respect to the Dirac point. A maximum carrier mobility of 11 200 cm 2 V - 1 s - 1 for this hBN/graphene/hBN heterostructure was measured at 4K, showing good device performance, in particular, after current annealing.