Dynamics and control of nonradiative excitons - free carriers mixture in GaAs/AlGaAs quantum wells

TL;DR

This study investigates the dynamics of nonradiative excitons in GaAs/AlGaAs quantum wells using pump-probe spectroscopy, revealing how exciton-carrier scattering influences exciton behavior and can be controlled via additional electron excitation.

Contribution

A simple model of exciton dynamics in quantum wells is developed, accurately describing experimental observations of exciton and carrier interactions under various excitation conditions.

Findings

Exciton-carrier scattering significantly affects exciton reservoir dynamics.

The developed model reproduces experimental exciton behavior and photoluminescence profiles.

Additional electron excitation can control exciton density in the reservoir.

Abstract

Dynamics of nonradiative excitons with large in-plane wave vectors forming a so-called reservoir is experimentally studied in a high-quality semiconductor structure containing a 14-nm shallow GaAs/Al$_{0.03}$Ga$_{0.97}$As quantum well by means of the non-degenerate pump-probe spectroscopy. The exciton dynamics is visualized via the dynamic broadening of the heavy-hole and light-hole exciton resonances caused by the exciton-exciton scattering. Under the non-resonant excitation free carriers are optically generated. In this regime the exciton dynamics is strongly affected by the exciton-carrier scattering. In particular, if the carriers of one sign are prevailing, they efficiently deplete the reservoir of the nonradiative excitons inducing their scattering into the light cone. A simple model of the exciton dynamics is developed, which considers the energy relaxation of photocreated electrons and holes, their coupling into excitons, and exciton scattering into the light cone. The model well reproduces the exciton dynamics observed experimentally both at the resonant and nonresonant excitation. Moreover, it correctly describes the profiles of the photoluminescence pulses studied experimentally. The efficient exciton-electron interaction is further experimentally verified by the control of the exciton density in the reservoir when an additional excitation creates electrons depleting the reservoir.