Search query: GaAs photoluminescence circular polarization

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abstract: We have studied the spin dynamics in self organized InAs/GaAs quantum dots by time resolved photoluminescence performed under strictly resonant excitation. At low temperature, we observe strictly no decay of both the linear and the circular luminescence polarization. This demonstrates that the carrier spins are totally frozen on the exciton lifetime scale.
author_names: M P Le Paillard

Xavier Marie

P Renucci

Thierry Amand

A Jbeli

J M Gerard
title: Spin relaxation quenching in semiconductor quantum dots.
venue: Physical review letters
year: 2001

abstract: The spin injection into GaAs has been studied for the ferromagnetic metal MnAs. Evidence for preferential minority spin injection is obtained from the circular polarization of the electroluminescence in GaAs/(In,Ga)As light emitting diodes (LED) The spin injection efficiency of 6% at the MnAs/GaAs interface is estimated on the basis of spin relaxation times extracted from time resolved photoluminescence measurements. This efficiency, as well as the preferential spin orientation, resembles very much the injection behavior found for epitaxial Fe layers. The results do not depend on the azimuthal orientation of the epitaxial MnAs injection layer.
author_names: Manfred Ramsteiner

H -Y Hao

Atsushi Kawaharazuka

H J Zhu

Martin Kastner

R Hey

L Daweritz

Holger T Grahn

K H Ploog
title: Electrical spin injection from ferromagnetic MnAs metal layers into GaAs
year: 2002

abstract: The magnitude and sign of the effective magnetic splitting factor g* for conduction electrons in GaAs/AlxGa(1 x)As quantum wells have been determined as a function of well width down to 5 nm. The experimental method is based on combined measurements of the decay time of photoluminescence and of the suppression of its circular polarization under polarized optical pumping in a magnetic field perpendicular to the growth axis (Hanle effect) Measurements as a function of hole sheet density in the wells reveal a transition from excitonic behavior with very small apparent g value for low density, to larger absolute values characteristic of free electrons at higher densities. For 20 nm wells g* for electrons is close to the bulk value 0.44) and increases for narrower wells passing through zero for well width close to 5.5 nm. A theoretical analysis based on three band k.p theory, including allowance for conduction band nonparabolicity and for wave function penetration into the barriers, gives a reasonable representation of the data, leading to the conclusion that g* in quantum wells has a value close to that of electrons in the bulk at the confinement energy above the band minimum.
title: Magnetic g factor of electrons in GaAs/AlxGa1 xAs quantum wells.
venue: Physical review. B, Condensed matter
year: 1991

abstract: We calculate for the first time the circular polarization of GaAs/\mathrm{Ga}}_{1\mathrm{\ensuremath{ \mathrm{x}\mathrm{Al}}_{\mathrm{x}$As quantum well photoluminescence taking into account the true nonparabolic valence band structure. Versus the excitation energy, we find high positive polarization for the transition n=1 heavy hole\char21{}to\char21{}conduction band transition and negative polarization at the onset of n=1 light hole\char21{}to\char21{}conduction band transition in qualitative agreement with experiments. We also study the \mathrm{Ga}}_{\mathrm{y}\mathrm{In}}_{1\mathrm{\ensuremath{ \mathrm{y}$As/InP system and predict no negative polarization in this case.
title: Variational calculation of polarization of quantum well photoluminescence.
venue: Physical review. B, Condensed matter
year: 1987

abstract: GaAs/AlAs pillar microcavities with elliptical cross section have been fabricated by molecular beam epitaxy, electron beam lithography, and reactive ion etching. We study their lowest energy confined photonic modes by photoluminescence, using a quantum box array placed inside the cavity as an internal broadband light source. Such an anisotropic cross section allows to split the twofold polarization degenerate fundamental mode of circular micropillars into a pair of orthogonal linearly polarized modes. Their energy splitting, which is well accounted for by a simple perturbative model, is studied experimentally and theoretically as a function of the eccentricity and average radius of the pillars. Splittings as large as 15 meV are observed, which is very encouraging for applications ranging from the improvement of the polarization locking in vertical cavity lasers to the fabrication of light emitting diodes with a better control of the spontaneous emission.
author_names: B Gayral

J M Gerard

Bernard Legrand

Eric Costard

Veronique Thierry-Mieg
title: Optical study of GaAs/AlAs pillar microcavities with elliptical cross section
year: 1998

abstract: We observed a circular photogalvanic effect (CPGE) in GaAs quantum wells at inter band excitation. The spectral dependence of the CPGE is measured together with that of the polarization degree of the time resolved photoluminescence. A theoretical model takes into account spin splitting of conduction and valence bands.
author_names: Vassilij V Bel'kov

Sergey D Ganichev

Petra Schneider

C G Back

Morgan Oestereich

Jens Rudolph

D Haegele

Leonid E Golub

Werner Wegscheider

Wilhelm Prettl
title: Circular photogalvanic effect at inter band excitation in semiconductor quantum wells
year: 2003

abstract: We report on optical orientation experiments in individual strain free GaAs quantum dots in AlGaAs grown by droplet epitaxy. Circularly polarized optical excitation yields strong circular polarization of the resulting photoluminescence at 4 K. Optical injection of spin polarized electrons into a dot gives rise to dynamical nuclear polarization that considerably changes the exciton Zeeman splitting (Overhauser shift) We show that the created nuclear polarization is bistable and we present a direct measurement of the buildup time of the nuclear polarization in a single GaAs dot in the order of 1 s.
author_names: Thomas Belhadj

Takashi Kuroda

Claire-Marie Simon

Thierry Amand

Takaaki Mano

Kazuaki Sakoda

Nobuyuki Koguchi

Xavier Marie

Bernhard Urbaszek
title: Optically monitored nuclear spin dynamics in individual GaAs quantum dots grown by droplet epitaxy
year: 2008

abstract: Luminescence spectra of interwell excitons in GaAs/AlGaAs double quantum wells with electric field tilted bands (n i n) structures were studied. In these structures the electron and the hole in the interwell exciton are spatially separated between neighboring quantum wells by a narrow AlAs barrier. Under resonant excitation by circularly polarized light the luminescence line of the interwell excitons exhibited appreciable narrowing as their concentration increased and the degree of circular polarization of the photoluminescence increased substantially. Under resonant excitation by linearly polarized light the alignment of the interwell excitons increased as a threshold process with increasing optical pumping. By analyzing time resolved spectra and the kinetics of the photoluminescence intensity under pulsed excitation it was established that under these conditions the rate of radiative recombination increases substantially. The observed effect occurs at below critical temperatures and is interpreted in terms of the collective behavior of the interwell excitons. Studies of the luminescence spectra in a magnetic field showed that the collective exciton phase is dielectric and in this phase the interwell excitons retain their individual properties.
author_names: A V Larionov

Vladislav B Timofeev

Jorn Marcher Hvam

K Soerensen
title: Interwell excitons in GaAs/AlGaAs double quantum wells and their collective properties
year: 2000

abstract: The authors have demonstrated by electroluminescence the injection of spin polarized electrons through Co/Al2O3/GaAs tunnel barrier into p doped InAs/GaAs quantum dots embedded in a p i n GaAs light emitting diode. The spin relaxation processes in the p doped quantum dots are characterized independently by optical measurements (time and polarization resolved photoluminescence) The measured electroluminescence circular polarization is about 15% at low temperature in a 2T magnetic field, proving an efficient electrical spin injection yield in the quantum dots. Moreover, this electroluminescence circular polarization is stable up to 70K.
author_names: Laurent Lombez

P Renucci

Pascal Gallo

P F Braun

Helene Carrere

P H Binh

Xavier Marie

Thierry Amand

Bernhard Urbaszek

J -L Gauffier

Thierry Camps

Alexandre Arnoult

Chantal Fontaine

Cyrile Deranlot

Richard Mattana

Henri Jaffres

J -M George
title: Electrical spin injection into p doped quantum dots through a tunnel barrier
year: 2007

abstract: The nuclear spin dynamics in an ensemble of singly charged (In,Ga)As/GaAs quantum dots has been studied at a temperature of 1.6 K. The effective magnetic field of nuclear polarization was detected through the circular polarization of quantum dot photoluminescence. The polarization is reduced if an external magnetic field compensates the nuclear field. To study the time evolution of the nuclear field, a photoluminescence pump probe technique has been developed, from which we find a complex behavior of the nuclear polarization dynamics; its rise is considerably slowed down when the effective field of polarized nuclei exceeds that of the nuclear spin fluctuations. A phenomenological model for the dynamics of a strongly coupled electron nuclear spin system has been developed, whose results qualitatively agree with the experimental data.
author_names: Roman V Cherbunin

S Y Verbin

Thomas Auer

D R Yakovlev

Dirk Reuter

Andreas Dirk Wieck

Il'ya Ya Gerlovin

I V Ignatiev

Dmitry V Vishnevsky

Manfred Bayer
title: Dynamics of the nuclear spin polarization by optically oriented electrons in a (In,Ga)As/GaAs quantum dot ensemble
year: 2009