High-Velocity Saturation in Graphene Encapsulated by Hexagonal Boron Nitride*

While mainly probed for its unique low-field electrical characteristics, graphene holds potential in practical device applications such as amplifiers or high-current interconnects. These applications rely on our understanding of the high electric field behavior and especially on our ability to minimize loss and maximize carrier velocities in graphene devices. Under high electric field, the drift velocity approaches a constant saturation velocity which can be limited by intrinsic or substrate phonons, heating, and substrate impurities. We present devices with graphene encapsulated by hexagonal boron nitride (hBN) which, due in part to the superior thermal conductivity and low impurity density of the hBN/graphene interface, produces saturation velocities higher than on all other common graphene substrates to date and suggest that hBN substrate phonons are the primary limiting factor for saturation velocity in our devices.