Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

International Conference on Luminescence - 1984

Exciton Holeburning in GaAs/GaAlAs Multiquantum Wells

John Hegarty, Michael D. Sturge

Published Jan 1, 1984• 1 citation
Publisher

Abstract

The lowest energy two-dimensional exciton in GaAs/GaAlAs multiquantum wells (MQW) is inhomogeneously broadened at low temperature by fluctuations in the layer width. The broadening permits probing of the excitons as a function of position within the inhomogeneous line[1]. At high densities interaction between the excitons becomes important and leads to saturation and to an increase of the homogeneous linewidth[2]. Using the picosecond pump/probe technique we have measured the saturation behavior as a function of exciton energy within the inhomogeneously broadened line. Figure 1 shows the transmission spectrum T of a weak narrowband probe (dotted) and the change in transmission ΔT of the probe induced by the presence of a pump for two different pump wavelength for 102 Å thick layers of GaAs separated by 200 Å layers of AlGaAs. An increase in transmission (holeburning) at the pump wavelength is observed showing that the interaction between resonant excitons is much stronger than between nonresonant excitons. The strength of the hole decreases rapidly on passing through the center of the line towards the high energy side. This is consistent with an increase in the homogeneous linewidth of the higher energy excitons[1,3]. By delaying the probe we measured the rate of decay of the hole which was found to depend strongly on pump intensity. At low intensity the hole lifetime approaches the luminescent lifetime but becomes shorter at exciton densities greater than ~109 excitons/cm2/layer. We attribute this to exciton-exciton scattering leading to spectral diffusion. The behavior was similar in 51 Å and 102 Å layers. In addition to holeburning, Figure 1 shows an increased absorption in the wings of the line whose shape is almost independent of pump wavelength and which is similar to that observed in bulk GaAs[2].

DOI
10.1364/icol.1984.fe17

Related papers

Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy

Rohan Singh

Correlated electron-hole pairs, or excitons, in semiconductor nanostructures have been studied extensively over the past few decades. The optical response of excitons is complicated due to inhomogeneous broadening, presence of multiple states, and exciton-exciton interactions. In this work we bring new perspectives to exciton physics in semiconductor quantum wells (QWs) through two-dimensional coherent spectroscopy (2DCS).\nThe effect of QW growth direction on the optical properties of excitons is explored by studying (110)-oriented GaAs QWs. The homogeneous and inhomogeneous linewidths of the heavy-hole exciton resonance are measured. By probing the optical nonlinear response for polarization along the in-plane crystal axes [1-10] and [001], we measure different homogeneous linewidths for the two orthogonal directions. This difference is found to be due to anisotropic excitation-induced dephasing, caused by a crystal-axis-dependent absorption coefficient. The extrapolated zero-excitation density homogeneous linewidth exhibits an activation-like temperature dependence.\nSpectral diffusion of excitons in (001)-oriented QWs has been studied. We show that the spectral diffusion characteristics depend strongly on the sample temperature. Spectral diffusion is generally assumed to follow the strong-redistribution approximation, partly because of lack of any evidence to the contrary. We find that this assumption is violated at low sample temperatures for excitons in QWs; high-energy excitons preferentially relax due to a negligible phonon population at low temperatures. The frequency-frequency correlation function is measured through a numerical fitting procedure to quantify spectral diffusion for sample temperatures $>20$ K.\nExciton-exciton interactions affect the light-matter interactions in QWs significantly. We present an intuitive and simple model for these interactions by treating excitons as interacting bosons. We show that the polarization-dependent exciton dephasing rate in GaAs quantum wells is due to the bosonic character of excitons. We fit slices from simulated spectra to those from the experimentally measured spectra and show that interference between two different quantum mechanical pathways results in a slower dephasing rate for co-circular and co-linear polarization of optical excitation pulses. This interference does not exist for cross-linearly polarized excitation pulses resulting in a faster dephasing rate. Additionally, we were able to separately quantify inter- and intra-mode interactions between excitons through exciton-density-dependent measurements.

•Jan 1, 2015•0 citations

Increase in Exciton Radiative Lifetime in GaAs Quantum Wells at High Exciton Density due to Exciton-Exciton Scattering

R. Eccleston, B. F. Feuerbacher, J. Kühl +2 more

We report time-resolved photoluminescence (TRPL) measurements of the radiative lifetime (τr) at 1.8K of resonantly excited heavy-hole excitons in a 27nm GaAs single quantum well as a function of exciton density. By the use of AlAs interface smoothing layers [1], the sample exhibits very little inhomogeneous broadening (≈0.15meV). The exciton centre of mass motion is therefore not significantly restricted by localisation in well width fluctuation islands. However, measurements of the exciton homogeneous linewidth (Γ h ) using time-resolved degenerate four wave mixing in the self-diffraction configuration (Fig.1) [2], additionally show that the sample imperfection scattering contribution to the Γ h of these delocalised excitons is also small (0.2meV). Thus, as indicated by the dependence of Γ h on exciton density (N x ), even at moderate exciton densities, exciton-exciton scattering is the dominant dephasing interaction within the photocreated exciton ensemble.

International Conference on Ultrafast Phenomena•Jan 1, 1992•0 citations

Two-color midinfrared saturation spectroscopy of intersubband transitions in multiquantum wells

Konstantin L. Vodopyanov, V. Chazapis, C. C. Phillips

A two-color pump–probe study of bound-to-bound and bound-to-quasibound intersubband transitions in InGaAs/AlGaAs and GaAs/AlGaAs multiquantum wells (MQW), with transition energies near 250 meV has been performed. Electrons were optically excited from the lowest to the upper subband using short midinfrared pulses of intensities up to 108 W/cm2 from a dual optical parametric generator. Differential transmission spectra, taken with the weaker probe pulses, evidence homogeneous line broadening behavior. From the width of the coherence peak, centered near the pump frequency, and arising from a dynamic population grating, the upper state lifetime (bound-to-bound transition) was found to be 0.6 ps, in good quantitative agreement with absorption saturation data.

Applied Physics Letters•Nov 25, 1996•13 citations

Effects of hole burning on pulse propagation in GaAs quantum wells

John Hegarty

Pulse time-of-flight measurements at the heavy exciton resonance in GaAs quantum wells reveal large pulse delays which are dependent on intensity and pulse spectral width. The measured pulse velocities are comparable to those seen in bulk GaAs and are as low as 6.7\ifmmode\times\else\texttimes\fi{}${10}^{6}$cm${\mathrm{s}}^{\ensuremath{-}1}$. We obtain quantitative agreement with a simple theory based on hole burning observed in the inhomogeneous exciton line, and we show that the measurements are useful in estimating exciton damping, under certain conditions.

Physical review. B, Condensed matter•Mar 15, 1982•46 citations

Nonlinear optical absorption and dynamics in quantum wells

Min Jiang, Hailin Wang, Duncan G. Steel

We present measurements of differential transmission and four-wave mixing in GaAs quantum well structures at 1.8 K near the inhomogeneously broadened lowest heavy-hole (hh1) exciton resonance using narrow band cw excitation. The data show an increase in absorption and an excitation lifetime of order 1–10 μs outside the spectral hole produced by the pump. The long lifetime and the experimentally determined absence of excitation spatial diffusion in this region suggests that optical absorption produces electron-hole pairs that are correlated but separately localized due to disorder. A phenomenological model is proposed to explain the nonlinear response based on two-photon absorption.

Applied Physics Letters•Sep 14, 1992•6 citations

Picosecond Nonlinear Optical Studies of Exciton Relaxation in Multiple Quantum Well Structures.

Michael D. Webb

This work presents new results of experimental studies of exciton relaxation in GaAs/AlGaAs multiple quantum well materials, using transient nonlinear laser spectroscopy techniques. In the low excitation regime, effective optical Bloch equations similar to the density matrix formalism of a two-level system describe the response. Solutions of these equations appropriate for three-pulse scattering studies are presented, along with a discussion of new experimental techniques used in this work. Non-ideal conditions present in the molecular beam epitaxy growth process introduce monolayer fluctuations in the quantum well thickness, leading to inhomogeneous broadening and exciton localization at sites of minimum energy. Localized excitons are separated in energy from extended, quasi-delocalized states by the mobility edge. Studies of localized exciton relaxation indicate that these excitons relax on a much slower timescale than delocalized excitons. The temperature dependence of the localized exciton relaxation rate shows that above 15K, the excitons are thermally activated to extended states above the mobility edge. Below 15K the excitons relax by phonon assisted migration between localization sites. For temperatures above 5K, and for exciton energies greater than 1 meV below line center, an extra dephasing mechanism characterizes the exciton relaxation. The inhomogeneous broadening of the exciton leads to the emission of stimulated photon echoes in the experimental geometry used in this work. The time-resolved emission demonstrates the stimulated photon echo nature at low excitation densities. At higher excitation densities, the decay dynamics is more complex. The time-resolved emission shows the presence of a stimulated photon echo and a free polarization decay. This unusual result suggests that both a homogeneous and an inhomogeneous exciton distribution comprise the exciton resonance. Exciton relaxation at low excitation densities represents the interaction of the exciton with the lattice. At higher excitation densities, exciton-exciton and exciton-free carrier interactions modify the relaxation rates. The dependence of the exciton relaxation rate on excitation density shows that many-body effects play an important role in the exciton physics. Free carrier interactions are more efficient at increasing the exciton relaxation rate; both types of interactions are more important in quantum well systems than in bulk materials.

•Jan 1, 1990•0 citations
The lowest energy two-dimensional exciton in GaAs/GaAlAs multiquantum wells (MQW) is inhomogeneously broadened at low temperature by fluctuations in the layer width. The broadening permits probing of the excitons as a function of position within the inhomogeneous line[1]. At high densities interaction between the excitons becomes important and leads to saturation and to an increase of the homogeneous linewidth[2]. Using the picosecond pump/probe technique we have measured the saturation behavior as a function of exciton energy within the inhomogeneously broadened line. Figure 1 shows the transmission spectrum T of a weak narrowband probe (dotted) and the change in transmission ΔT of the probe induced by the presence of a pump for two different pump wavelength for 102 Å thick layers of GaAs separated by 200 Å layers of AlGaAs. An increase in transmission (holeburning) at the pump wavelength is observed showing that the interaction between resonant excitons is much stronger than between nonresonant excitons. The strength of the hole decreases rapidly on passing through the center of the line towards the high energy side. This is consistent with an increase in the homogeneous linewidth of the higher energy excitons[1,3]. By delaying the probe we measured the rate of decay of the hole which was found to depend strongly on pump intensity. At low intensity the hole lifetime approaches the luminescent lifetime but becomes shorter at exciton densities greater than ~109 excitons/cm2/layer. We attribute this to exciton-exciton scattering leading to spectral diffusion. The behavior was similar in 51 Å and 102 Å layers. In addition to holeburning, Figure 1 shows an increased absorption in the wings of the line whose shape is almost independent of pump wavelength and which is similar to that observed in bulk GaAs[2].
Correlated electron-hole pairs, or excitons, in semiconductor nanostructures have been studied extensively over the past few decades. The optical response of excitons is complicated due to inhomogeneous broadening, presence of multiple states, and exciton-exciton interactions. In this work we bring new perspectives to exciton physics in semiconductor quantum wells (QWs) through two-dimensional coherent spectroscopy (2DCS).\nThe effect of QW growth direction on the optical properties of excitons is explored by studying (110)-oriented GaAs QWs. The homogeneous and inhomogeneous linewidths of the heavy-hole exciton resonance are measured. By probing the optical nonlinear response for polarization along the in-plane crystal axes [1-10] and [001], we measure different homogeneous linewidths for the two orthogonal directions. This difference is found to be due to anisotropic excitation-induced dephasing, caused by a crystal-axis-dependent absorption coefficient. The extrapolated zero-excitation density homogeneous linewidth exhibits an activation-like temperature dependence.\nSpectral diffusion of excitons in (001)-oriented QWs has been studied. We show that the spectral diffusion characteristics depend strongly on the sample temperature. Spectral diffusion is generally assumed to follow the strong-redistribution approximation, partly because of lack of any evidence to the contrary. We find that this assumption is violated at low sample temperatures for excitons in QWs; high-energy excitons preferentially relax due to a negligible phonon population at low temperatures. The frequency-frequency correlation function is measured through a numerical fitting procedure to quantify spectral diffusion for sample temperatures >20>20>20 K.\nExciton-exciton interactions affect the light-matter interactions in QWs significantly. We present an intuitive and simple model for these interactions by treating excitons as interacting bosons. We show that the polarization-dependent exciton dephasing rate in GaAs quantum wells is due to the bosonic character of excitons. We fit slices from simulated spectra to those from the experimentally measured spectra and show that interference between two different quantum mechanical pathways results in a slower dephasing rate for co-circular and co-linear polarization of optical excitation pulses. This interference does not exist for cross-linearly polarized excitation pulses resulting in a faster dephasing rate. Additionally, we were able to separately quantify inter- and intra-mode interactions between excitons through exciton-density-dependent measurements.
We report time-resolved photoluminescence (TRPL) measurements of the radiative lifetime (τr) at 1.8K of resonantly excited heavy-hole excitons in a 27nm GaAs single quantum well as a function of exciton density. By the use of AlAs interface smoothing layers [1], the sample exhibits very little inhomogeneous broadening (≈0.15meV). The exciton centre of mass motion is therefore not significantly restricted by localisation in well width fluctuation islands. However, measurements of the exciton homogeneous linewidth (Γ h ) using time-resolved degenerate four wave mixing in the self-diffraction configuration (Fig.1) [2], additionally show that the sample imperfection scattering contribution to the Γ h of these delocalised excitons is also small (0.2meV). Thus, as indicated by the dependence of Γ h on exciton density (N x ), even at moderate exciton densities, exciton-exciton scattering is the dominant dephasing interaction within the photocreated exciton ensemble.
A two-color pump–probe study of bound-to-bound and bound-to-quasibound intersubband transitions in InGaAs/AlGaAs and GaAs/AlGaAs multiquantum wells (MQW), with transition energies near 250 meV has been performed. Electrons were optically excited from the lowest to the upper subband using short midinfrared pulses of intensities up to 108 W/cm2 from a dual optical parametric generator. Differential transmission spectra, taken with the weaker probe pulses, evidence homogeneous line broadening behavior. From the width of the coherence peak, centered near the pump frequency, and arising from a dynamic population grating, the upper state lifetime (bound-to-bound transition) was found to be 0.6 ps, in good quantitative agreement with absorption saturation data.
Pulse time-of-flight measurements at the heavy exciton resonance in GaAs quantum wells reveal large pulse delays which are dependent on intensity and pulse spectral width. The measured pulse velocities are comparable to those seen in bulk GaAs and are as low as 6.7\ifmmode\times\else\texttimes\fi{}106{10}^{6}106cm${\mathrm{s}}^{\ensuremath{-}1}$. We obtain quantitative agreement with a simple theory based on hole burning observed in the inhomogeneous exciton line, and we show that the measurements are useful in estimating exciton damping, under certain conditions.
We present measurements of differential transmission and four-wave mixing in GaAs quantum well structures at 1.8 K near the inhomogeneously broadened lowest heavy-hole (hh1) exciton resonance using narrow band cw excitation. The data show an increase in absorption and an excitation lifetime of order 1–10 μs outside the spectral hole produced by the pump. The long lifetime and the experimentally determined absence of excitation spatial diffusion in this region suggests that optical absorption produces electron-hole pairs that are correlated but separately localized due to disorder. A phenomenological model is proposed to explain the nonlinear response based on two-photon absorption.
This work presents new results of experimental studies of exciton relaxation in GaAs/AlGaAs multiple quantum well materials, using transient nonlinear laser spectroscopy techniques. In the low excitation regime, effective optical Bloch equations similar to the density matrix formalism of a two-level system describe the response. Solutions of these equations appropriate for three-pulse scattering studies are presented, along with a discussion of new experimental techniques used in this work. Non-ideal conditions present in the molecular beam epitaxy growth process introduce monolayer fluctuations in the quantum well thickness, leading to inhomogeneous broadening and exciton localization at sites of minimum energy. Localized excitons are separated in energy from extended, quasi-delocalized states by the mobility edge. Studies of localized exciton relaxation indicate that these excitons relax on a much slower timescale than delocalized excitons. The temperature dependence of the localized exciton relaxation rate shows that above 15K, the excitons are thermally activated to extended states above the mobility edge. Below 15K the excitons relax by phonon assisted migration between localization sites. For temperatures above 5K, and for exciton energies greater than 1 meV below line center, an extra dephasing mechanism characterizes the exciton relaxation. The inhomogeneous broadening of the exciton leads to the emission of stimulated photon echoes in the experimental geometry used in this work. The time-resolved emission demonstrates the stimulated photon echo nature at low excitation densities. At higher excitation densities, the decay dynamics is more complex. The time-resolved emission shows the presence of a stimulated photon echo and a free polarization decay. This unusual result suggests that both a homogeneous and an inhomogeneous exciton distribution comprise the exciton resonance. Exciton relaxation at low excitation densities represents the interaction of the exciton with the lattice. At higher excitation densities, exciton-exciton and exciton-free carrier interactions modify the relaxation rates. The dependence of the exciton relaxation rate on excitation density shows that many-body effects play an important role in the exciton physics. Free carrier interactions are more efficient at increasing the exciton relaxation rate; both types of interactions are more important in quantum well systems than in bulk materials.