Phonon and Electronic Non-radiative Decay of Excitons in Carbon Nanotubes

TL;DR

This paper theoretically analyzes non-radiative decay mechanisms of excitons in carbon nanotubes, finding that localized excitons decay faster and proposing a doping-dependent decay mechanism with lifetimes of 5-100 ps.

Contribution

It introduces a new doping-dependent decay mechanism for excitons in carbon nanotubes and compares theoretical decay rates with experimental data.

Findings

Multi-phonon decay of free excitons is too slow to match experiments.

Localized excitons have significantly shorter decay lifetimes.

Doping enables a new decay pathway with 5-100 ps lifetimes.

Abstract

We investigate theoretically the rates of non-radiative decay of excited semiconducting nanotubes by a variety of decay mechanisms and compare with experimental findings. We find that the multi-phonon decay (MPD) of free excitons is too slow to be responsible for the experimentally observed lifetimes. However, MPD lifetimes of localized excitons could be 2-3 orders of magnitude shorter. We also propose a new decay mechanism that relies on a finite doping of nanotubes and involves exciton decay into an optical phonon and an intraband electron-hole pair. The resulting lifetime is in the range of 5 to 100 ps, even for a moderate doping level.