共查询到20条相似文献,搜索用时 31 毫秒
1.
We report experimental studies on exciton spin coherence induced via Coulomb correlations between excitons with opposite spins, including correlations associated with unbound as well as bound exciton pairs. Electromagnetically induced transparency resulting from the spin coherence is demonstrated in the transient optical response in GaAs quantum wells. 相似文献
2.
We present a computer simulation of exciton–exciton scattering in a quantum well. Specifically, we use quantum Monte Carlo techniques to study the bound and continuum states of two excitons in a 10 nm wide GaAs/Al0.3Ga0.7As quantum well. From these bound and continuum states we extract the momentum-dependent phase shifts for s-wave scattering. A surprising finding of this work is that a commonly studied effective-mass model for excitons in a 10 nm quantum well actually supports two bound biexciton states. The second, weakly bound state may dramatically enhance exciton–exciton interactions. We also fit our results to a hard-disk model and indicate directions for future work. 相似文献
3.
Jang Hee Chu Jung-Chul Seo Eun-Joo Shin Sung-Kyu Yu Dongho Kim Young-Nam Hwang Seung-Han Park Ung Kim Pjotr S. Kop'ev 《Optical and Quantum Electronics》1995,27(5):387-393
The photoluminescence linewidths and excition lifetimes of free excitons in GaAs/AlGaAs multiple quantum wells were systematically investigated as a function of temperature, quantum well width, and carrier density. The experimental results showed that the exciton decay processes were strongly related to the linewidth of the exciton and the exciton binding energy. 相似文献
4.
Photoluminescence attributed to excitons bound to neutral impurities has been observed from GaAs quantum wells in AlxGa1?xAs-GaAs heterostructures grown by molecular beam epitaxy. The quantum wells were either doped with [Be] ≈ 1017 cm-3 or Zn-diffused. At low temperatures both single and multiple quantum wells exhibited this extrinsic luminescence which is ascribed to the radiative recombination of the n=1 ground state heavy hole exciton E1h bound to a neutral acceptor Ao. The dissociation energy ED of the Ao-E1h complex is obtained directly from the measured separation of this extrinsic peak from the intrinsic E1h free exciton peak. For 46Å wide GaAs wells, ED=6.5meV and ED decreases with increasing well width. 相似文献
5.
Binding energies of Wannier excitons in a quantum well structure consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga1?xAlxAs are calculated using a variational approach. Due to reduction in symmetry along the axis of growth of these quantum well structures and the presence of band discontinuities at the interfaces, the degeneracy of the valence band of GaAs is removed leading to two exciton systems, namely, the heavy hole exciton and the light hole exciton. The variations of the binding energies of these two excitons as a function of the size of the GaAs quantum wells for various values of the heights of the potential barrier are calculated and their behavior is discussed. 相似文献
6.
V. B. Timofeev A. I. Tartakovskii A. I. Filin D. Birkedal J. Hvam 《Physics of the Solid State》1998,40(5):767-769
Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and
spatially indirect excitons in GaAs/AlGaAs superlattices having different electron and hole miniband widths in high magnetic
fields perpendicular to the heterolayers. The ground state of the indirect excitons formed by electrons and holes which are
spatially distributed among neighboring quantum wells is found to lie between the ground 1s state of the direct excitons and the threshold of the continuum of dissociated exciton states in the minibands. The indirect
excitons have a substantial oscillator strength when the binding energy of the exciton exceeds the scale of the width of the
resulting miniband. It is shown that a high magnetic field shifts a system of symmetrically bound quantum wells toward weaker
bonding. At high exciton concentrations, spatially indirect excitons are converted into direct excitons through exciton-exciton
collisions.
Fiz. Tverd. Tela (St. Petersburg) 40, 833–836 (May 1998) 相似文献
7.
A. I. Tartakovskii V. B. Timofeev V. G. Lysenko D. Birkedal J. Hvam 《Journal of Experimental and Theoretical Physics》1997,85(3):601-608
Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and
spatially indirect excitons in GaAs/AlaAs superlattices, with different widths of the electron and hole minibands, located
in a high magnetic field perpendicular to the heterolayers. It is found that the ground state of the indirect excitons formed
by electrons and holes and spatially separated between neighboring quantum wells lies between the ls ground state of the direct excitons and the continuum threshold for dissociated exciton states in the minibands. Indirect
excitons in superlattices have a significant oscillator strength when the binding energy of the exciton exceeds the order
of the width of the resulting miniband. The behavior of the binding energy of direct and indirect heavy hole excitons during
changes in the tunneling coupling between the quantum wells is established. It is shown that a strong magnetic field, which
intensifies the Coulomb interaction between the electron and hole in an exciton, weakens the bond in a system of symmetrically
bound quantum wells. The spatially indirect excitons studied here are analogous to first order Wannier-Stark localized excitons
in superlattices with inclined bands (when an electrical bias is applied), but in the present case the localization is of
purely Coulomb origin.
Zh. éksp. Teor. Fiz. 112, 1106–1118 (September 1997) 相似文献
8.
On the binding energies of excitons in polar quantum well structures in a weak electric field
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The binding energies of excitons in quantum well structures subjected to an applied uniform electric field by taking into account the exciton longitudinal optical phonon interaction is calculated. The binding energies and corresponding Stark shifts for Ⅲ-Ⅴ and Ⅱ-Ⅵ compound semiconductor quantum well structures have been numerically computed. The results for GaAs/A1GaAs and ZnCdSe/ZnSe quantum wells are given and discussed. Theoretical results show that the exciton-phonon coupling reduces both the exciton binding energies and the Stark shifts by screening the Coulomb interaction. This effect is observable experimentally and cannot be neglected. 相似文献
9.
N. N. Ledentsov R. Nötzel P. S. Kop'ev K. Ploog 《Applied Physics A: Materials Science & Processing》1992,55(6):533-536
Hot exciton relaxation is observed in GaAs/Al
x
Ga1–x
As multiple quantum wells. The photolumnescence excitation spectra of the localized exciton emission at low temperatures and excitation densities are composed of narrow equidistant peaks exactly separated by the GaAs LO-phonon energy (36 meV). The relaxation mechanism via LO-phonons is found to be important for localized excitons in multiple quantum wells with GaAs layer thicknesses of about 50 Å, where pronounced alloy fluctuations in the barriers provide a strong additional lateral potential which suppresses the dissociation of hot excitons. 相似文献
10.
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
11.
Z. P. Wang X. X. Liang X. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):41-46
Polaron effects on excitons in parabolic quantum wells are
studied theoretically by using a variational approach with the so-called
fractional dimension model. The numerical results for the exciton binding
energies and longitudinal-optical phonon contributions in
GaAs/Al0.3Ga0.7As parabolic quantum well structures are obtained as functions of the well width. It is shown that the exciton binding energies
are obviously reduced by the electron (hole)-phonon interaction and the polaron effects are un-negligible. The results demonstrate
that the fractional-dimension variational theory is effectual in the investigations of excitonic polaron problems in parabolic
quantum wells. 相似文献
12.
T. S. Shamirzaev 《Physics of the Solid State》2018,60(8):1554-1567
The behavior of excitons in heterostructures with indirect-gap GaAs/AlAs quantum wells and (In, Al)As/AlAs quantum dots is discussed. The possibilities of controlled change of the exciton radiative recombination time in the range from dozens of nanoseconds to dozens of microseconds, experimental study of the spin dynamics of long-lived localized excitons, and use of the optical resonant methods for exciting the indirect-band exciton states are demonstrated. 相似文献
13.
《Superlattices and Microstructures》1995,17(2):201-212
Transient photoluminescence of GaAs/AlGaAs quantum wires and quantum dots formed by strain confinement is studied as a function of temperature. At low temperature, luminescent decay times of the wires and dots correspond to the radiative decay times of localized excitons. The radiative decay time can be either longer or shorter than that of the host quantum well, depending on the size of the wires and dots. For small wires and dots (∼ 100 nm stressor), the exciton radiative recombination rate increases due to lateral confinement. Exciton localization due to the fluctuation of quantum well thickness plays an important role in the temperature dependence of luminescent decay time and exciton transfer in quantum wire and dot structures up to at least ∼ 80 K. Lateral exciton transfer in quantum wire and dot structures formed by laterally patterning quantum wells strongly affects the dynamics of wire and dot luminescence. The relaxation time of hot excitons increases with the depth of strain confinement, but we find no convincing evidence that it is significantly slower in quasi 1-D or 0-D systems than in quantum wells. 相似文献
14.
E. C. Ferreira J. A. P. da Costa J. A. K. Freire G. A. Farias V. N. Freire 《Applied Surface Science》2002,190(1-4):191-194
Confined excitons in non-abrupt GaAs/AlxGa1−xAs single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al0.3Ga0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces. 相似文献
15.
A series of GaAs/AlAs multiple-quantum wells doped with Be is grown by molecular beam epitaxy. The photoluminescence spectra are measured at 4, 20, 40, 80, 120, and 200 K, respectively. The recombination transition emission of heavy-hole and light-hole free excitons is clearly observed and the transition energies are measured with different quantum well widths. In addition, a theoretical model of excitonic states in the quantum wells is used, in which the symmetry of the component of the exciton wave function representing the relative motion is allowed to vary between the two- and threedimensional limits. Then, within the effective mass and envelope function approximation, the recombination transition energies of the heavy- and light-hole excitons in GaAs/AlAs multiple-quantum wells are calculated each as a function of quantum well width by the shooting method and variational principle with two variational parameters. The results show that the excitons are neither 2D nor 3D like, but are in between in character and that the theoretical calculation is in good agreement with the experimental results. 相似文献
16.
A. F. Adiyatullin V. V. Belykh V. I. Kozlovsky V. S. Krivobok V. P. Martovitsky S. N. Nikolaev 《Journal of Experimental and Theoretical Physics》2012,115(5):885-896
Exciton states in Zn(Cd)Se/ZnMgSSe quantum wells with different diffusion spreading of interfaces are studied by optical spectroscopy methods. It is shown that the emission spectrum of quantum wells at low temperatures is determined by free excitons and bound excitons on neutral donors. The nonlinear dependence of the stationary photoluminescence intensity on the excitation power density and the biexponential luminescence decay are explained by the neutralization of charged defects upon photoexcitation of heterostructures. With the stationary illumination on, durable (about 40 min) reversible changes in the reflection coefficient near the exciton resonances of quantum wells are observed. It is shown that, along with the shift of exciton levels, the spreading of heteroboundaries leads to three effects: an increase in the excitonphonon interaction, an increase in the energy shift between the emission lines of free and bound excitons, and a decrease in the decay time of exciton luminescence in a broad temperature range. The main reasons for these effects are discussed. 相似文献
17.
《Superlattices and Microstructures》1987,3(1):9-12
We have studied by means of low temperature photoluminescence (PL) and photocurrent spectroscopy the effects of an external electric field on the excitons in GaAs quantum wells confined between GaAlAs. Increasing the field causes a Stark shift of the excitons toward lower energies with a simultaneous quenching in the PL intensity. At moderate fields, we find very good agreement (better than 0.5 meV) between the light- and heavy-hole exciton energies obtained by PL and photocurrent measurements. A significant deviation in energy of the PL relative to the photocurrent is observed at high fields, manifesting the increase in the contributions of impurity-bound excitons to the PL lineshape. A detailed PL study of the Stark shift as a function of well thickness has also been performed. The results show an increasing Stark shift with increasing well thickness, amounting to 110 meV for a 230 Å-wide well at a field of 105 V/cm. For very wide wells (∼ 1000 Å) the behavior of bulk GaAs is recovered: the excitons become ionized before large Stark shifts can be observed. Variational calculations have been carried out and shown to account for the experimental observations of both the Stark shift and the quenching of the PL. In this light, we will discuss the mechanisms governing the optical properties of quantum wells under an external electric field. 相似文献
18.
《Superlattices and Microstructures》1995,17(2):187-191
The exciton wavefunction in parabolic quantum wells is calculated using variational techniques and effective mass theory. The influences of the potential shape and of confinement on the exciton binding energies are studied. The results are in good agreement with previous calculations. The oscillator-strength of excitons in GaAs/Ga1-xAlxAS quantum wells has a maximum value very close to the cross-over from three to two dimensions. 相似文献
19.
A technique that makes it possible to investigate the mechanisms of phase relaxation of excitons in GaAs single quantum wells
has been developed using resonant reflection spectroscopy. The dependence of the oscillator strength of the exciton transition
on the quantum well thickness has been measured in the thickness range 9.1–30.0 nm. It has been demonstrated that the oscillator
strength with a high accuracy does not depend on the temperature in the range 8–90 K. The temperature dependence of the homogeneous
broadening has been measured, and the inhomogeneous broadening of the resonance exciton line has been determined. A nonmonotonic
dependence of the spectral broadening of the exciton line on the intensity of the resonant excitation at a temperature of
8 K has been revealed for the sample with a high-quality quantum well. It has been established that an increase in the excitation
level by five orders of magnitude above the linear limit leads to an insignificant change in the oscillator strength of the
exciton transition and to a multiple broadening of the spectral line profile. 相似文献
20.
Radiative lifetime of an exciton in a GaAs quantum well (QW) is controlled by high-density excitons, which restrict the exciton coherence through scattering. In order to circumvent the phase space filling effect of high-density excitons, we have prepared a QW structure in such a way that a reservoir for high-density excitons is separated from the QW. The lifetime increases (up to 30%) with the exciton density in the reservoir and saturates at 1×1017/cm3. The upper bound lifetime is determined by the excitonic relative motion. 相似文献