Direct measure of the exciton formation in quantum wells from time resolved interband luminescence

TL;DR

This study uses time-resolved luminescence to directly measure exciton formation times in high-quality quantum wells, revealing density dependence and non-equilibrium conditions at low densities.

Contribution

It provides the first direct measurement of exciton formation time in quantum wells with high spectral and temporal resolution.

Findings

Exciton formation time depends on carrier density as predicted by theory.

A minority of excitons dominate the luminescence signal.

No thermodynamical equilibrium is observed at low densities.

Abstract

We present the results of a detailed time resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform this experiment with a spectral resolution and a sensitivity of the set-up allowing to keep the observation of these two separate contributions over a broad range of times and densities. This allows us to directly evidence the exciton formation time, which depends on the density as expected from theory. We also evidence the dominant contribution of a minority of excitons to the luminescence signal, and the absence of thermodynamical equilibrium at low densities.