Impact Ionization and Carrier Multiplication in Graphene

TL;DR

This paper presents a model for impact ionization in graphene, demonstrating its significance in carrier generation and its effects on transistor behavior, including an up-kick in drain current and altered electric field distribution.

Contribution

The authors develop a self-consistent model for impact ionization in graphene and incorporate it into transistor simulations, revealing new insights into high-bias behavior.

Findings

Drain current exhibits an up-kick at high biases

Carrier generation influences electric field distribution

Model aligns with recent experimental data

Abstract

We develop a model for carrier generation by impact ionization in graphene, which shows that this effect is non-negligible because of the vanishing energy gap, even for carrier transport in moderate electric fields. Our theory is applied to graphene field effect transistors for which we parametrize the carrier generation rate obtained previously with the Boltzmann formalism [A. Girdhar and J. Leburton, Appl. Phys. Lett. 99, 229903 (2011)] to include it in a self-consistent scheme and compute the transistor I-V characteristics. Our model shows that the drain current exhibits an "up-kick" at high drain biases, which is consistent with recent experimental data. We also show that carrier generation affects the electric field distribution along the transistor channel, which in turn reduces the carrier velocity.