Resonant femtosecond emission from quantum well excitons: The role of Rayleigh scattering and luminescence

Benoît Marie Joseph Deveaud
1997
Journal paper

We study the ultrafast properties of secondary radiation of semiconductor quantum wells under resonant excitation. We show that the exciton density dependence allows one to identify the origin of secondary radiation. At high exciton densities, the emission is due to incoherent luminescence with a rise time determined by exciton-exciton scattering. For low densities, when the distance between excitons is much larger than their diameter, the temporal shape is independent of density and rises quadratically, in excellent agreement with recent theories for resonant Rayleigh scattering.

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Benoît Marie Joseph Deveaud
1997
Journal paper

Abstract

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https://infoscience.epfl.ch/record/110995?ln=en

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Quantum well

A quantum well is a potential well with only discrete energy values. The classic model used to demonstrate a quantum well is to confine particles, which were initially free to move in three dimensio

Exciton

An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force. It is an electrically neutral quasiparticle that exists in ins

Quantum

In physics, a quantum (: quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a physical property can be "quantized" is re

Resonant Rayleigh scattering on quantum well excitons: Theory and experiment

Benoît Marie Joseph Deveaud, Vincenzo Savona

Time-resolved up-conversion measurements of secondary emission from multiple quantum wells under resonant femtosecond excitation are reported for GaAs multiple quantum wells with qualitatively different interface disorder. The transient resonant Rayleigh scattering presents very peculiar features such as a long-lived signal and a nonmonotonic behaviour, which cannot be explained by a classical model. A microscopic model is proposed, where the quantum mechanical equation for the microscopic polarization is solved numerically assuming a random two-dimensional potential with spatial correlation, and a phenomenological dephasing time. The model succeeds in reproducing the shape of the transients. It is shown that, for typical parameters of GaAs quantum well excitons, quantum mechanical features are essential in the description of the scattered intensity. The observed features of the signal are interpreted in terms of polarization beatings due to the energy quantization of exciton levels lying within the same fluctuation site.

2000

Dynamics of trion formation in GaAs quantum wells

Jean Berney, Benoît Marie Joseph Deveaud, Lars Kappei, François Morier-Genoud, Marcia Portella Oberli

We show a double path mechanism for the formation of charged excitons (trions); they are formed through bi- and trimolecular processes. This directly implies that both negatively and positively charged excitons coexist in a quantum well, even in the absence of excess carriers. The model is substantiated by time-resolved photoluminescence experiments performed on a very high quality InxGa1-xAs quantum well sample, in which the photoluminescence contributions at the energy of the trion and exciton and at the band edge can be clearly separated and traced over a broad range of times and densities. The unresolved discrepancy between the theoretical and experimental radiative decay time of the exciton in a doped semiconductor quantum well is explained by the same model.

2009

Femtosecond dynamics of secondary radiation formation from quantum well excitons

Benoît Marie Joseph Deveaud

The time-resolved secondary emission of resonantly created excitons in GaAs quantum wells is studied using femtosecond up-conversion spectroscopy. The behaviour of the rise and decay of the secondary emission and reflectivity in quantum welts is strongly dependent upon the disorder at the interfaces, the exciton density and the temperature. In the case of low densities and temperatures the emission is independent of the exciton density and rises quadratically in time, in excellent agreement with recent theory for Rayleigh scattering from two-dimensional excitons subjected to disorder. These rise times are compared directly with T-2 times measured by time-integrated four-wave mixing (FWM). The comparison of the dynamics displayed in time-resolved secondary radiation and time-integrated FWM provide a clear understanding of the coherence properties of QW excitons in the first few picoseconds after excitation. High-contrast oscillations that are due to quantum beats between the heavy- and light-hole Is-states are seen. The visibility decay at very low densities is long tau(HL) = 25 ps and is related to the action of potential fluctuations on the scattering of heavy-hole and light-hole excitons. (C) 1998 Elsevier Science B.V. All rights reserved.

1998