Density-dependent exciton radiative lifetimes in GaAs quantum wells

Eccleston, Richard; Feuerbacher, B. F.; Kühl, J.; Rühle, W. W.; Ploog, K.

doi:10.1103/physrevb.45.11403

Cited by 78 publications

(33 citation statements)

References 14 publications

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“…The rise and decay times in the both signals estimated by fitting with a single exponential function are 4 and 120 ps, respectively. This decay time is shorter than the values reported in the multiple quantum well samples by the time-resolved photoluminescence-measurement [6].…”

Section: Resultsmentioning

confidence: 49%

Spectrally resolved nonlinear optical response of weakly confined excitons under femtosecond laser pulse excitation in GaAs thin films

Kojima

Isu

Ishi‐Hayase

et al. 2006

Phys. Status Solidi (c)

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We have investigated the dynamical properties of the weakly confined excitons in GaAs thin films by a transient grating method (three-beam four-wave mixing) with the use of femtosecond-laser pulses. The time-domain signals under the exciton-excitation conditions show a nonlinear optical response with a rise time of 4 ps and a long decay time of 120 ps. Moreover, in the case of that the probe pulse is parallel polarized to the two excitation pulses, the ultrafast optical response comparable to the pulse width appears. These characteristics of the nonlinear optical response is different from the experimental results by the picosecond-laser-pulse excitation. The spectra of the transient grating signals at the various time delays show several peaks at the energies, which agree with the energies of excitons confined in the thin films. This fact demonstrates that the characteristics of the nonlinear optical response of the weakly confined excitons are drastically changed by the spectral width of the excitation laser-pulse.1 Introduction Dynamical properties and optical nonlinearity of excitons in semiconductor bulk crystals, multiple quantum wells, and quantum dots have been extensively studied from the viewpoints of physics of ultrafast phenomena and application to ultrafast optical devices [1,2]. Recently, in the weak confinement regime, it was reported that optical nonlinearity and fast response of excitons due to the interaction with the radiation field are remarkably enhanced by the double resonance in energy and size [3][4][5]. However, to our knowledge, many experiments for the nonlinear optical response of the weakly confined excitons have been performed by using laser pulses with a width of a few picoseconds and narrow spectrum width which resonantly excites a single exciton state.If femtosecond-laser pulses with a broader spectral width are used to generate nonlinear optical response of weakly confined excitons, multiple exciton states which are energetically close each other are excited. Thus, we may reveal the effect of the spectral width of the excitation pulse on the nonlinear optical response of the weakly confined excitons by comparing with the results of picosecond-laser pulse-excitations. In the present work, we have investigated the nonlinear optical response of the weakly confined excitons in GaAs thin films by using a transient grating method with 160-fs pulse-duration for the first time. We have found that the transient grating signals of the GaAs thin films under the femtosecond-pulse-excitation conditions indicate a rise time of 4 ps and a decay time of 120 ps. In addition, the ultrafast optical response comparable to the pulse width is observed when all of the pulses of the excitation and probe are copolarized. The origin of the nonlinear optical response is discussed from an aspect of the spectra of the transient grating signals.

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Section: Resultsmentioning

confidence: 49%

Spectrally resolved nonlinear optical response of weakly confined excitons under femtosecond laser pulse excitation in GaAs thin films

Kojima

Isu

Ishi‐Hayase

et al. 2006

Phys. Status Solidi (c)

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“…Figure 12 and estimates with Eq. ͑30͒ clearly show that the majority of optical experiments [16][17][18][19][20][21][22]27 with GaAs QWs are undertaken under conditions when the incoherent scattering rate ␥ x can easily achieve the values of ␥ x tr or ␥ x tr . Another important question is to what extent the presented model and results are robust against inhomogeneous broadening which is practically inevitable in QW structures.…”

Section: ͑28͒mentioning

confidence: 99%

Strong and weak coupling limits in optics of quantum well excitons

Creatore

Ivanov

2008

Phys. Rev. B

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A transition between the strong ͑coherent͒ and weak ͑incoherent͒ coupling limits of resonant interaction between quantum well ͑QW͒ excitons and bulk photons is analyzed and quantified as a function of the incoherent damping rate ␥ x caused by exciton-phonon and exciton-exciton scatterings. For confined QW polaritons, a second, anomalous, ␥ x -induced dispersion branch arises and develops with increasing ␥ x . In this case, the strong-weak coupling transition is attributed to ␥ x = ␥ x tr or ␥ x tr , when the intersection of the normal and damping-induced dispersion branches occurs either in ͕k ʈ ,Im͓͔ ,Re͓͔͖ coordinate space ͑in-plane wave vector k ʈ is real͒ or in ͕ ,Im͓k ʈ ͔ ,Re͓k ʈ ͔͖ coordinate space ͑frequency is real͒, respectively. For the radiative states of QW excitons, i.e., for radiative QW polaritons, the transition is described as a qualitative change of the photoluminescence spectrum at grazing angles along the QW structure. We show that the radiative corrections to the QW exciton states with in-plane wave vector k ʈ approaching the photon cone, i.e., at Ϸ1.5 meV.

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“…Thus the transition dipole strength and resulting radiative decay rate is a linear function of the coherence volume. [18][19][20][21][22] Feldmann et al demonstrated this linear relationship experimentally through the dependence of exciton lifetime on the temperaturedependent homogeneous spectral linewidth. 18 Later, a similar relationship was demonstrated between exciton radiative lifetime and QD size for CuCl microcrystals.…”

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confidence: 99%

Inhibited recombination of charged magnetoexcitons

et al. 1998

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Time-resolved photoluminescence measurements show that the decay time for charged excitons in a GaAs twodimensional electron gas increases by an order of magnitude at high magnetic fields. Unlike neutral excitons, the charged exciton center-of-mass is spatially confined in a "magnetically-adjustable quantum dot" by the cyclotron orbit and the quantum well. The inhibited recombination is explained by a reduced phase coherence volume of the magnetically-confined charged excitons.PACS numbers: 71.35. Ji, 8.47.+p, 73.20.D Charged excitons or "trions" were first identified in optical absorption experiments on electron-doped CdTe quantum well (QW) structures through their polarization properties in a magnetic field. 1 The negatively charged exciton (X − ) transition in a narrow QW was manifest in the spectra as a peak lying several meV below the uncharged exciton (X 0 ) peak. Although both X 0 and X − transitions may had been observed previously in PL spectra of GaAs QWs, the high electron density precluded their identification. 2 In hindsight, it is not surprising that the recently identified X − is often the most common exciton found in a system with excess electrons, similar to the X 0 in a system without excess electrons. An X 0 in the presence of excess electrons becomes polarized by a nearby electron and binds the electron by a dipolar attraction. The properties of X − transitions in GaAs QWs have been explored in several recent experimental 3-7 and theoretical [8][9][10][11][12] studies.An interesting facet of the charged exciton that has yet to be explored is the confinement produced by the cyclotron motion in a magnetic field. The X − complex (two electrons plus one hole) is singly-charged and a magnetic field confines the X − center-of-mass motion to a cyclotron orbit, unlike the neutral exciton (X 0 ) which is free to move in a magnetic field. This will be referred to as the magnetically-confined charged exciton (MCX). A magnetic field applied perpendicular to a twodimensional (2D) QW effectively confines the exciton to a quantum dot (QD) whose size is adjustable with magnetic field. The 3D MCX volume, defined roughly by the QW width and the area of the cyclotron orbit in the plane of QW, is inversely proportional to the perpendicular magnetic field, V M CX ∝ 1/B ⊥ . At high magnetic fields this volume is typically smaller than QDs currently available via patterned nanostructures.The purpose of the present study is to examine the radiative recombination of excitons confined in these MCX QDs. Exciton recombination times were determined by measuring the photoluminescence (PL) decay times in low-density GaAs/AlGaAs electron gases in magnetic fields to 18 T, at temperatures 0.5-7 K. At low temperatures, the X − decay time was found to increase by an order of magnitude for increasing perpendicular magnetic field. In contrast, the recombination is rapid for both the X − in fields applied in the plane of the QW and for the uncharged X 0 . In the latter two cases the exciton is not confined to a QD. The linear d...

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Density-dependent exciton radiative lifetimes in GaAs quantum wells

Cited by 78 publications

References 14 publications

Spectrally resolved nonlinear optical response of weakly confined excitons under femtosecond laser pulse excitation in GaAs thin films

Spectrally resolved nonlinear optical response of weakly confined excitons under femtosecond laser pulse excitation in GaAs thin films

Strong and weak coupling limits in optics of quantum well excitons

Inhibited recombination of charged magnetoexcitons

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