Abstract
Dynamic wavelength tunability has long been the holy grail of photodetector technology. Because of its atomic thickness and unique properties, graphene opens up new paradigms to realize this concept, but so far this has been elusive experimentally. Here we employ detailed quantum transport modeling of photocurrent in graphene field-effect transistors (including realistic electromagnetic fields) to show that wavelength tunability is possible by dynamically changing the gate voltage. We reveal the phenomena that govern the behavior of this type of device and show significant departure from the simple expectations based on vertical transitions. We find strong focusing of the electromagnetic fields at the contact edges over the same length scale as the band-bending. Both of these spatially-varying potentials lead to an enhancement of non-vertical optical transitions, which dominate even in the absence of phonon or impurity scattering. We also show that the vanishing density of states near the Dirac point leads to contact blocking and a gate-dependent modulation of the photocurrent. Several of the effects discussed here should be applicable to a broad range of one- and two-dimensional materials and devices.
Highlights
Modeling efforts have considered different possibilities for tunable graphene photodetectors based on multiple graphene layers, such as bilayer graphene photogating[14] and tunneling between two separate graphene layers[15] or nanoribbons[16]
We address the challenges of identifying promising tunable detector designs and the necessity for more detailed quantum modeling by developing and implementing a non-equilibrium quantum transport approach for photocurrent calculations in graphene devices, including realistic electromagnetic fields
We find that translational symmetry breaking due to spatially-varying band-bending and electromagnetic fields leads to a dominance of non-vertical transitions that significantly change the behavior expected from pure vertical transitions and Fermi blocking[17]
Summary
Modeling efforts have considered different possibilities for tunable graphene photodetectors based on multiple graphene layers, such as bilayer graphene photogating[14] and tunneling between two separate graphene layers[15] or nanoribbons[16]. These exciting results, based on macroscopic transport equations appropriate for long-channel devices, show the promise of devices based on multiple graphene layers. We address the challenges of identifying promising tunable detector designs and the necessity for more detailed quantum modeling by developing and implementing a non-equilibrium quantum transport approach for photocurrent calculations in graphene devices, including realistic electromagnetic fields. We show that the vanishing density of states at the graphene Dirac point leads to a gate-dependent modulation of the photocurrent due to a contact blocking effect
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