Nonlinear behaviour of the nonradiative exciton reservoir in quantum wells

TL;DR

This study investigates the nonlinear dynamics of a nonradiative exciton reservoir in GaAs/AlGaAs quantum wells, revealing how various processes influence exciton behavior at different densities and temperatures through time-resolved spectroscopy.

Contribution

It provides a detailed experimental and theoretical analysis of the nonlinear behavior of the nonradiative exciton reservoir, extending previous models to include new dynamic processes.

Findings

Reservoir dynamics are highly nonlinear due to competing processes.

Characteristic rates depend on excitation power and temperature.

Reservoir exciton densities remain below Mott transition levels.

Abstract

Excitons and free charge carriers with large wave vectors form a nonradiative reservoir, which can strongly affect properties of bright excitons due to the exciton-exciton and exciton-carrier interactions. In the present work, the dynamics of quasiparticles in the reservoir at different areal densities is experimentally studied in a GaAs/AlGaAs quantum well using a time-resolved reflectance spectroscopy of nonradiative broadening of exciton resonances. The population of the reservoir is controlled either by the excitation power or by the temperature of the structure under study. The dynamics is quantitatively analyzed in the framework of the model developed earlier [Kurdyubov et al., Phys. Rev. B {\bf 104}, 035414 (2021)]. The model considers several dynamic processes, such as scattering of photoexcited excitons into the reservoir, dissociation of excitons into free charge carriers and the reverse process, carrier-induced exciton scattering into the light cone depleting the reservoir, thermally activated nonradiative losses of charge carriers. We have found that competition of these processes leads to highly nonlinear dynamics of reservoir excitons, although their density is far below the exciton Mott transition densities. Characteristic rates of the processes and their dependencies on the excitation power and the temperature are determined.