We report mid-infrared photocurrent spectra of graphene nanoribbon arrays on SiO2 dielectrics showing dual signatures of the substrate interaction. First, hybrid polaritonic modes of graphene plasmons and dielectric surface polar phonons produce a thermal photocurrent in graphene with spectral features that are tunable by gate voltage, nanoribbon width, and light polarization. Secondly, phonon-polaritons associated with the substrate are excited, which indirectly heat up the graphene leading to a graphene photocurrent with fixed spectral features. Models for other commonly used substrates show that the responsivity of graphene infrared photodetectors can be tailored to specific mid-IR frequency bands by the choice of the substrate.
@article{arxiv.1407.7554,
title = {Substrate Sensitive Mid-Infrared Photoresponse in Graphene},
author = {Marcus Freitag and Tony Low and Luis Martin-Moreno and Wenjuan Zhu and Francisco Guinea and Phaedon Avouris},
journal= {arXiv preprint arXiv:1407.7554},
year = {2014}
}