Gate-Controlled Nonlinear Conductivity of Dirac Fermion in Graphene Field-Effect Transistors Measured by Terahertz Time-Domain Spectroscopy

Abstract

We present terahertz spectroscopic measurements of Dirac fermion dynamics from a large-scale graphene that was grown by chemical vapor deposition and on which carrier density was modulated by electrostatic and chemical doping. The measured frequency-dependent optical sheet conductivity of graphene shows electron-density-dependence characteristics, which can be understood by a simple Drude model. In a low carrier density regime, the optical sheet conductivity of graphene is constant regardless of the applied gate voltage, but in a high carrier density regime, it has nonlinear behavior with respect to the applied gate voltage. Chemical doping using viologen was found to be efficient in controlling the equilibrium Fermi level without sacrificing the unique carrier dynamics of graphene.

Terahertz wafer-scale mobility mapping of graphene on insulating substrates without a gate

“…Consistent with previous observations in THz-TDS [18,24,25] and FTIR [10,15,[26][27][28] studies of graphene, we find the conductance dynamics to be well described by the Drude model, given by…”

Robust mapping of electrical properties of graphene from terahertz time-domain spectroscopy with timing jitter correction

“…This is usually done by only fitting to the real part of s σ [3,5,9]. Here, both real and imaginary parts of and to full fits to uncorrected data.…”

“…Terahertz time-domain spectroscopy (THz-TDS) is a non-contact measurement technique that can be used to determine electrical properties of conducting thin films such as graphene [1][2][3][4]. The non-contact approach is advantageous for in-line characterization and quality-control for industrial integration of graphene, especially when compared to standard field-effect measurements on graphene that require additional and intrusive fabrication steps for device processing.…”

Optical modulators with 2D layered materials

“…4c,d). In this THz spectral range, the demonstrated modulation speed is on the order of KHz or MHz range [85][86][87][88][89][90] , which is limited by the large size (~mm, comparable to the THz beam waist) of the device.…”