Non-equilibrium charge dynamics in graphene-based devices encapsulated by boron nitride

Boron nitride (BN) encapsulation has become standard for creating ultra-high quality devices with van der Waals (vdW) materials. BN is generally assumed to be a featureless dielectric for the encapsulated vdW material, or a source of a moiré potential when rotationally aligned with graphene. However, in this work we show that non-equilibrium dynamics of charged defect states in BN can have a range of impacts on graphene-based device performance beyond what has been appreciated previously. In misaligned graphene/BN devices without a moiré, we find that charged defect states in BN can introduce hysteresis and telegraph noise in measurements of the resistance of the charge neutrality point, when transport is dominated by percolation through charge puddles. In other devices, we see an anomalous gate screening behavior that persists above room temperature and in structures as thick as bulk graphite. We find that the screening effect diminishes over timescales of days or longer, pointing to the possibility that defect-based trap states in the BN play an important role. We will discuss possible microscopic mechanisms, the potential role of introducing a moiré pattern, and the possibility of achieving new device functionalities by engineering defect states in BN.