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1.
The influence of photoexcited carriers on the dynamics of the absorption spectra of GaAs/AlxGa1−2x
As multilayer quantum wells is investigated experimentally. It is found that at quasiparticle densities all the way up to
1011 cm−2 the saturation of the excitonic absorption is due to both a decrease of oscillator strength and broadening of the excitonic
lines. It is shown that in the case of femtosecond resonance laser exci-tation the decrease of oscillator strength is due
to free electron-hole pairs, while the broadening and energy shift of the excitonic lines are due to the exciton-exciton interaction.
The lifetimes of free electron-hole pairs and excitons (≈65 ps and ≈410 ps, respectively) are determined from the exponential
decrease of the change in the oscillator strength and in the width and energy position of the excitonic lines.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 139–144 (10 August 1997) 相似文献
2.
S. I. Gubarev O. V. Volkov V. A. Koval’skii D. V. Kulakovskii I. V. Kukushkin 《JETP Letters》2002,76(9):575-578
The spectrum of excitonic excited states in GaAs/AlGaAs quantum wells of different width is studied together with its change due to the screening of electron-hole interaction by two-dimensional electrons. The exciton binding energy decreases sharply with an increase in the concentration of two-dimensional electrons. The temperature dependence of screening parameters is studied for the ground and excited excitonic states down to ultralow temperatures T=50 mK. 相似文献
3.
《Superlattices and Microstructures》1995,17(4):389-392
We report on a novel peak, the F-line, observed in photoluminescence spectra of GaAs/AlGaAs quantum wells (QWs) with various donor layer positions and concentrations. The F-line is well-defined and red shifted by approximately 1.3 meV (dependent on the experimental conditions) relatively the free exciton (FE) in a 200 Å wide QW. The F-line exhibits a strong magnetic field dependence. The enhanced intensity with increasing field is due to an increasing wave function overlap caused by the enhanced localization of the involved charge carriers. In accordance, the derived thermal activation energy for the F-line is magnetic field dependent. The F-line exhibits a diamagnetic shift as expected for an excitonic transition and splits into four components with increasing magnetic field. Another associated higher energy peak, the E-line, is observed preferably in the presence of a magnetic field, between the heavy hole- and light hole-FE in PL excitation spectra. The E-line also exhibits a striking magnetic field and temperature dependence. The observed properties of the F-line with a striking dependence on the excitation intensity, magnetic field and temperature are consistent with the observation of an exciton bound at the negatively charged D- donor state or a negatively charged X- exciton. 相似文献
4.
O. V. Volkov V. E. Zhitomirskii I. V. Kukushkin V. E. Bisti K. von Klitzing K. Eberl 《JETP Letters》1997,66(11):766-772
The temperature and magnetic-field dependences of the recombination line of multiparticle excitonic complexes in undoped and
lightly doped GaAs/AlGaAs quantum wells are investigated. These dependences have previously been attributed to free charged
excitons (trions). It is shown that this line corresponds to a bound state of a complex, specifically, to an exciton bound
on a neutral donor in a barrier. It is found that as the temperature or pump power is raised, there appear in the recombination
spectrum not only a cyclotron replica shifted downward in energy but also a replica which is symmetrically shifted upwards
in energy by an amount equal to the cyclotron energy and which is due to emission from an excited state of an impurity complex.
The behavior of the cyclotron replicas is studied as a function of the electron density and temperature.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 11, 730–735 (10 December 1997) 相似文献
5.
O. V. Volkov V. E. Zhitomirskii I. V. Kukushkin K. von Klitzing K. Eberl 《JETP Letters》1998,67(9):744-750
The recombination spectra of excitons and excitonic complexes in un-doped GaAs/AlGaAs single quantum wells are investigated.
It is shown on the basis of a study of the magnetic-field dependence of the emission spectra and the degree of optical orientation
in zero magnetic field and on the basis of electrooptic measurements that not only the density but also the sign of the charge
carriers in a well depend strongly on the photoexcitation energy. It is shown on the basis of a comparative analysis of the
spin splitting of the recombination lines of free and bound excitons that the recombination line which was attributed earlier
to a positively charged exciton corresponds to the recombination of an exciton bound on a neutral acceptor.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 707–713 (10 May 1998) 相似文献
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9.
We have observed very high-frequency, highly reproducible magneto-oscillations in modulation doped GaAs/AlGaAs quantum well structures. The oscillations are periodic in an inverse magnetic field (1/B) and their amplitude increases with temperature up to T approximately 700 mK. Being initially most pronounced around the filling factor nu=1/2, they move towards lower nu with increasing T. Front and back-gating data imply that these oscillations require a coupling to a parallel conducting layer. A comparison with existing oscillation models renders no explanation. 相似文献
10.
11.
The pump-probe experimental method is used to investigate the effect of photoexcited carriers on the dynamics of the exciton
absorption spectra of GaAs / AlxGa1–x
As-multilayer quantum wells. Use of the method of moment analysis for processing the results makes it possible to identify
the simultaneous contribution of changes in oscillator strength and width of the exciton lines in the saturation of exciton
absorption. It was found that the oscillator strength recovers its initial value in the course of the first 100–130 ps, whereas
broadening and energy-shift of the exciton lines is observed for 700–800 ps. These are the first experimental measurements
of the excitation densities at which the oscillator strength of the excitonic state saturates when the latter is perturbed
only by free-electron-hole pairs, and when it is perturbed only by other excitons.
Fiz. Tverd. Tela (St. Petersburg) 40, 1130–1133 (June 1998) 相似文献
12.
《Superlattices and Microstructures》1994,16(4):331-334
We report on the carrier dynamics in n-type double-barrier quantum well structures in an electric field. Both the intersubband and interband photocurrents, excited by long-wavelength (4μm) and short-wavelength (0.5μm) radiation, respectively, show a photovoltaic asymmetry with respect to the applied field. This asymmetry arises from an internal field due to an asymmetric dopant distribution with respect to the well centers. Time-dependent photoluminescence measurements allow us to determine the field dependence of the electron and hole capture times. 相似文献
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14.
M.A.G. Soler J. Depeyrot P.C. Morais J.A.N.T. Soares L.M.R. Scolfaro E.C.F. da Silva R. Enderlein G. Weimann G. Trankle 《Superlattices and Microstructures》1997,21(4):581-585
In this work we investigated the optical control of the bidimensional electron gas density in a single asymmetric quantum well using, for the first time, photoreflectance. We performed our measurements at 80 and 300 K as a function of the power density of the pump beam. Under strong illumination, the bidimensional electron gas density is washed out of the quantum well and under a dark condition, it reaches its maximum value. The variation of the optical transitions observed in our photoreflectance spectra was related to the induced changes of the band profile in between these two limiting cases. 相似文献
15.
M. Yu. Akimov I. V. Kukushkin S. I. Gubarev S. V. Tovstonog J. Smet K. von Klitzing W. Wegscheider 《JETP Letters》2000,72(9):460-463
Dimensional magnetoplasma resonance is observed and studied in a spatially confined, two-dimensional hole system in (001) GaAs/AlGaAs single quantum wells. From the analysis of the field dependence of the magnetoplasma resonance on the diameter of the 2D system, the semiclassical cyclotron hole mass is determined. Its value is found to be equal to 0.26m 0 (m 0 is the free electron mass), which considerably exceeds the theoretically predicted value. A method is proposed for a direct determination of the concentration and mobility of 2D holes from the analysis of the magnetoplasma resonance. 相似文献
16.
The dynamics of excitons and trions in GaAs/AlGaAs heterostructures with shallow quantum wells is studied in time-resolved
photoluminescence experiments carried out with different repetition rates of picosecond pump pulses for the cases of intrawell,
above-barrier, and“two-color” excitation. It is established that excess charge carriers of one type accumulated in the quantum
wells under above-barrier excitation play a key role in the formation and dynamics of the exciton-trion system and determine
its composition and kinetic properties. The lifetime of excess charge carriers in the quantum wells, estimated from the experimental
data, exceeds 10 μs. 相似文献
17.
《Superlattices and Microstructures》1995,17(1):23-26
Shake-up transitions involving QW hole subbands have been observed as satellites in selective photoluminescence spectra of undoped GaAs/AlGaAs QWs. These shake-up transitions are explained in terms of an interaction between localized exciton and valence-band hole states attached to the QW subbands, in which holes are shaken up from the n=1 heavy hole subband to higher subbands, either the n=1 light hole subband or the n=2 heavy hole subband. The required localization is due to the interface roughness; thus these new transitions are of intrinsic origin. From the observation of the intersubband shake-up processes we derive direct information about the hole inter-subband energies. Furthermore, the satellite intensity is strikingly enhanced in the presence of a magnetic field due to an increasing exciton localization related to the compression of its wave function in the field. The exciton wave function compression continues until its radius in the plane of the well is comparable with the radius of the "flat island" characterized by constant QW width. Accordingly, from the magnetic field dependence of the shake-up satellite intensity we can roughly estimate the size of the "flat islands" and consequently probe the interface roughness. 相似文献
18.
S. V. Poltavtsev V. V. Ovsyankin B. V. Stroganov Yu. K. Dolgikh S. A. Eliseev Yu. P. Efimov V. V. Petrov 《Optics and Spectroscopy》2008,105(4):511-516
The mechanisms of exciton coherence relaxation in GaAs quantum wells in the linear mode have been experimentally investigated. An experimental technique has been developed for measuring the total phase relaxation rate, rates of reversible and temperature-irreversible excitonic phase relaxation, and the radiative decay rate Γ R of excitonic polarization. The experimental values of Γ R for a quantum well of specified thickness, obtained for a series of samples, have a spread not larger than 15%. This accuracy made it possible to estimate the shape of the dependence of Γ R on the well thickness L Z . It is experimentally found that Γ R is temperature-independent up to 80 K. 相似文献
19.
T. Nguyen-Quang J.-M. Jancu P. Voisin 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):352
A quantitative comparison between different model calculations of valence band states in GaAs/AlGaAs heterostructures is presented. We demonstrate that a 14-band k.p Hamiltonian using a completely new parameterization based on fits of the tight-binding band structure leads to energy dispersion relations in excellent agreement with experiment, whereas previous parameterizations result in significant deviations. The relevance of the present results to the calculation of spin-related phenomena is discussed. 相似文献
20.
O. V. Volkov S. V. Tovstonog I. V. Kukushkin K. von Klitzing K. Eberl 《JETP Letters》1999,70(9):595-601
The localization of negatively charged excitons on isolated charged donors, located in a barrier at various fixed distances L from the heteroboundary, is investigated in isolated GaAs/AlGaAs quantum wells. The energy shift of the cyclotron replica in the emission spectra of a localized excitonic complex is studied as a function of L. It is shown that in undoped samples charged excitons localize on residual donors at distances L>350 Å on account of the formation of D ? complexes at shorter distances. It is established that a cyclotron replica arises with the recombination of an excited state and not the ground state, as previously thought, of an excitonic complex. 相似文献