Inelastic Scattering and Current Saturation in Graphene

TL;DR

This study models transport in graphene on polar substrates, revealing that self-heating reduces saturated velocity and suggesting that thinner insulators could enhance current capacity, with detailed analysis of phonon effects.

Contribution

It provides a comprehensive Boltzmann transport model including various scattering mechanisms and predicts the impact of thermal effects and substrate properties on graphene's saturated velocity.

Findings

Saturated velocity is weakly dependent on carrier density and substrate type.

Self-heating significantly reduces the saturated velocity from theoretical predictions.

Thinner insulator layers can increase saturated current in graphene devices.

Abstract

We present a study of transport in graphene devices on polar insulating substrates by solving the Bolzmann transport equation in the presence of graphene phonon, surface polar phonon, and Coulomb charged impurity scattering. The value of the saturated velocity shows very weak dependence on the carrier density, the nature of the insulating substrate, and the low-field mobility, varied by the charged impurity concentration. The saturated velocity of 4 - 8 x 10^7 cm/s calculated at room temperature is significantly larger than reported experimental values. The discrepancy is due to the self-heating effect which lowers substantially the value of the saturated velocity. We predict that by reducing the insulator oxide thickness, which limits the thermal conductance, the saturated currents can be significantly enhanced. We also calculate the surface polar phonon contribution to the low-field mobility as a function of carrier density, temperature, and distance from the substrate.