We study the Fermi energy level dependence of nonlinear terahertz (THz) transmission of gated multi-layer and single-layer graphene transferred onto sapphire and quartz substrates. The two samples represent two limits of low-field impurity scattering: short-range neutral and long-range charged impurity scattering, respectively. We observe an increase in the transmission as the field amplitude is increased due to intraband absorption bleaching starting at fields above 8 kV/cm. This effect arises from a field-induced reduction in THz conductivity that depends strongly on the Fermi energy. We account for intraband absorption using a free carrier Drude model that includes neutral and charged impurity scattering as well as optical phonon scattering. We find that although the Fermi-level dependence in the monolayer and five-layer samples is quite different, both exhibit a strong dependence on the field amplitude that cannot be explained on the basis of an increase in the lattice temperature alone. Our results provide a deeper understanding of transport in graphene devices operating at THz frequencies and in modest kV/cm field strengths where nonlinearities exist.
@article{arxiv.1508.00624,
title = {High field response of gated graphene at THz frequencies},
author = {Hadi Razavipour and Hassan A. Hafez and Ibraheem Al-Naib and Wayne Yang and Pierre Lévesque and Abdeladim Guermoune and Francois Blanchard and Xin Chai and Denis Ferachou and Richard Martel and Michael Hilke and Marc M. Dignam and Tsuneyuki Ozaki and David G. Cooke},
journal= {arXiv preprint arXiv:1508.00624},
year = {2016}
}