Effect of Coulomb scattering on graphene conductivity

TL;DR

This paper investigates how Coulomb scattering influences graphene's conductivity, revealing that electron-hole interactions dominate in intrinsic conditions and that defect-related scattering explains experimental variations.

Contribution

It provides a theoretical derivation showing the universal intrinsic conductivity of graphene and explains experimental discrepancies through defect density dependence on Fermi energy.

Findings

Intrinsic conductivity is universal and independent of temperature.

Electron-hole scattering dominates in pure graphene.

Defect density varies with Fermi energy, affecting conductivity.

Abstract

The effect of Coulomb scattering on graphene conductivity in field effect transistor structures is discussed. Inter-particle scattering (electron-electron, hole-hole, and electron-hole) and scattering on charged defects are taken into account in a wide range of gate voltages. It is shown that an intrinsic conductivity of graphene (purely ambipolar system where both electron and hole densities exactly coincide) is defined by strong electron-hole scattering. It has a universal value independent of temperature. We give an explicit derivation based on scaling theory. When there is even a small discrepancy in electron and hole densities caused by applied gate voltage the conductivity is determined by both strong electron-hole scattering and weak external scattering: on defects or phonons. We suggest that a density of charged defects (occupancy of defects) depends on Fermi energy to explain a sub-linear dependence of conductivity on a fairly high gate voltage observed in experiments. We also eliminate contradictions between experimental data obtained in deposited and suspended graphene structures regarding graphene conductivity.