Photon-induced tunneling in graphene-boron nitride-graphene heterostructures

Abstract

Graphene is a material that has generated much interest due to its many unique electronic and optical properties. In this work, we present optoelectronic measurements performed on ultrathin graphene-boron nitride-graphene heterostructures. Scanning photocurrent spectroscopy allows us to explore the tunneling behavior of these devices as a function of both photon energy and bias voltage. Tunneling through the boron nitride insulator is found to be dramatically enhanced by the presence of light, showing a high-bias behavior that can be well described using Fowler-Nordheim tunneling. These measurements indicate that tunneling is dominated by photoexcited positive charge carriers (holes) with an intrinsic barrier height and effective mass of 1.33eV and 1.1 9me, respectively. These numbers agree well with theoretical calculations of the offset between the top of the valence band in boron nitride and the charge neutrality point in graphene, and the effective mass of holes in boron nitride. Moreover, a peak in the conductance was observed at zero bias voltage, indicating the presence of thermionic emission near the charge neutrality point..