Energy relaxation during hot-exciton transport in quantum wells: Direct observation by spatially resolved phonon-sideband spectroscopy

TL;DR

This study directly observes the energy relaxation of hot excitons during their transport in ZnSe quantum wells using spatially resolved phonon-sideband spectroscopy, revealing excitons remain hot over several micrometers and classical diffusion models are inadequate.

Contribution

It provides a direct measurement of hot exciton energy relaxation during real-space transport in quantum wells using spatially resolved spectroscopy.

Findings

Excitons remain hot over several micrometers during transport.

Classical diffusion models do not describe excitonic transport on this scale.

Energy relaxation occurs during exciton transport, as observed through LO-phonon sideband evolution.

Abstract

We investigate the energy relaxation of excitons during the real-space transport in ZnSe quantum wells by using microphotoluminescence with spatial resolution enhanced by a solid immersion lens. The spatial evolution of the LO-phonon sideband, originating from the LO-phonon assisted recombination of hot excitons, is measured directly. By calculating the LO-phonon assisted recombination probability, we obtain the nonthermal energy distribution of excitons and observe directly the energy relaxation of hot excitons during their transport. We find the excitons remain hot during their transport on a length scale of several micrometers. Thus, the excitonic transport on this scale cannot be described by classical diffusion.