First Principles Based Mobility Estimation of Graphene

Abstract

Electron-phonon coupling (EPC) plays a vital role in detecting transport properties (e.g. mobility) of any material. First principles-based estimation of the mobility for any new material could act as a useful guideline for experimentalist. Inclusion of EPC in quantum transport models that involves non-equilibrium Greens function (NEGF) formalism with density functional theory (DFT), is numerically demanding. Because of this computational burden, some approximations are made such as phonon can be described within harmonic approximation which neglects non-harmonic part. However, at room temperature there will be non-harmonic contribution. In a new technique, molecular dynamics (MD) is combined with Landauer transport equation, for the estimation of mobility. Molecular dynamics simulation inherently includes non-harmonic e ect. Temperature dependent mobility is calculated by combining classical MD simulation with DFT calculation. The main purpose of the MD is to generate the snapshot of the thermally disordered solid. From each of these Snapshots, transmission spectrum is calculated. These transmissions are averaged over a number of samples and conductance is calculated using Landauer approach to yield good results. The charge concentration for this mobility is calculated using Fermi-Dirac statistics. Using calculated resistivity obtained from di erent temperature and the carrier concentration, temperature dependent mobility is estimated. However, such technique has so far been demonstrated for bulk and one-dimensional materials. In this work we investigate if the same technique is applicable for two dimensional materials. We apply the same technique to estimate the temperature dependent mobility of graphene. Our results are in good agreement with the mobility estimated using other first principles-based techniques (DFT+Boltzmann Transport Equation).