共查询到20条相似文献,搜索用时 576 毫秒
1.
The exciton-polariton transfer and absorption in regular and disordered structures with a finite number of quantum wells are studied theoretically. The transfer matrix method is invoked in the exciton resonance region to calculate the reflectivity, transmissivity, and absorptivity spectra, as well as the integrated absorptivity as a function of the γ/Γ0 ratio of the parameters of nonradiative and radiative damping of quasi-two-dimensional excitons. It is shown that the integrated absorptivity as a function of γ (temperature) follows a universal pattern, more specifically, it increases monotonically from zero at γ = 0 to saturate at γ/Γ0 ? 1. Because the exciton-polariton absorption being single mode, the integrated absorptivity in Bragg quantum-well structures is substantially lower than that in short-period structures, in which absorption involves the whole spectral multitude of modes. The intrawell disorder associated with fluctuations in the frequencies of exciton excitation in quantum wells enhances the integrated absorptivity to the level typical of light absorption with no resonance among excitons of different quantum wells. The interwell disorder originating from fluctuations in quantum-well separation likewise leads to an increase in the integrated absorptivity. 相似文献
2.
V. D. Kulakovskii L. V. Kulik A. L. Yablonskii A. B. Dzyubenko N. A. Gippius S. G. Tikhodeev A. Forchel 《Physics of the Solid State》1998,40(5):740-742
We have measured the photoluminescence spectra and photoluminescence excitation spectra of magnetic excitons in InGaAs/GaAs
near-surface quantum wells in a magnetic field. We have quantitatively investigated the effect of dielectric enhancement of
excitons in quantum wells brought about by decreasing the thickness of the barrier layer, both in a magnetic field and without.
Fiz. Tverd. Tela (St. Petersburg) 40, 806–808 (May 1998) 相似文献
3.
A. V. Larionov V. B. Timofeev J. Hvam K. Soerensen 《Journal of Experimental and Theoretical Physics》2000,90(6):1093-1104
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. 相似文献
4.
N.E. Kaputkina Yu.E. Lozovik 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):291
Direct and indirect excitons in coupled quantum wells and in coupled quantum dots are studied. We consider excitons with two-dimensional, quasi-two-dimensional and three-dimensional carriers. Problems were investigated for a wide range of characteristic parameters—confining to potential steepness, distances between quantum wells or dots, effective width of wells and magnetic fields. The mutual influence of the controlling parameters of the problem on exciton properties is analyzed. Energy and wave function spectra were calculated and dispersion law and effective masses were obtained. 相似文献
5.
V. P. Kochereshko V. N. Kats A. V. Platonov R. A. Suris G. E. Cirlin A. D. Buravlev Yu. B. Samsonenko L. Besombes C. Le Gal H. Mariette 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(5):722-725
The results of a study into the photoluminescence spectra of a set of quantum dots based on GaAs enclosed in AlGaAs nanowires are presented. The steady state and time resolved spectra of photoluminescence under optical excitation both from an array of quantum wires/dots and a single quantum wire/dot have been measured. In the photoluminescence spectra of single quantum dots, emission lines of excitons, biexcitons and tritons have been found. The binding energy of the biexciton in the studied structures was deduced to be 8 meV. 相似文献
6.
XIE Wen-Fang 《理论物理通讯》2006,45(3):565-567
In this paper, a negatively charged exciton trapped by a
spherical parabolic quantum dot has been investigated. The
energy spectra of low-lying states are calculated by means of
matrix diagonalization. The important feature of
the low-lying states of the negatively charged excitons in a spherical
quantum dot is obtained via an analysis of the energy spectra. 相似文献
7.
A clear signature of enhanced backscattering of excitons is observed in the directional resonant Rayleigh scattering of light from localized two-dimensional excitons in disordered quantum wells. Its spectral dependence and time dynamics are measured and theoretically predicted in a quantitative way. The intensity enhancement has a large momentum span extending beyond the external light emission cone. This is a consequence of the small localization length of the exciton as a massive particle probed close to the band bottom. The localization length can be controlled by the photon kinetic energy. This constitutes a qualitative difference to backscattering phenomena in other branches of physics. 相似文献
8.
Studies of the photoluminescence spectra of spatially indirect excitons in coupled quantum wells revealed that the emission
has a directional pattern dependent on the external electric field and pumping power. The experimentally detected correlation
between the spectral emission parameters of spatially indirect excitons, namely, the concentration (phase state) of such excitons,
the line half-width, the degree of linear polarization, and the existence of a directional pattern, permits a suggestion that
the spontaneous photoluminescence of spatially indirect excitons in the condensed state is of a coherent nature. 相似文献
9.
Noriaki Tsurumachi Chang-Sik Son Tae Geun Kim Kazunori Hikosaka Kazuhiro Komori Mutsuo Ogura 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):300
We investigated the temperature dependence of the time-resolved photoluminescence (PL) spectra of high-density InGaAs/AlGaAs quantum wire (QWR) distributed-feedback laser structure on a submicron grating. A red-shift of peak in the time-resolved PL after photo-excitation was observed due to the relaxation of the photo-generated excitons from the entire QWR to localized centers at 10 K. On the other hand, at 60 K, no red-shift in the time-resolved PL spectra was observed since the localization centers are thermally activated and the excitons are delocalized. 相似文献
10.
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
11.
Keiichi Edamatsu 《Journal of luminescence》1996,70(1-6):377-385
We investigated the dynamics of confined excitons and biexcitons in CuCl quantum dots in an NaCl matrix by using subpicosecond pump and probe absorption spectra, and time-resolved luminescence spectra. Then temporal changes of the absorption, optical gain, and luminescence are interpreted in relation to the exciton dynamics. The optical nonlinearity is discussed in terms of the exciton-exciton interaction in the quantum dot. 相似文献
12.
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
13.
The energies of the electron and hole weak-coupling polarons are determined in quantum rings of finite width in a uniform magnetic field. It is shown that polaron corrections exhibit oscillatory behavior as a function of a magnetic field. The effect of polaron corrections on the absorption and emission spectra of light by excitons in a quantum ring is considered. 相似文献
14.
A theory of quasi-stationary states and lifetimes of electrons, holes, and excitons in an open cylindrical semiconductor quantum wire containing a quantum dot surrounded by two identical antidots (with potential barriers of finite height) is developed using the scattering matrix method. The energy spectra and lifetimes of electrons, holes, and excitons in a β-HgS/β-CdS/β-HgS/β-CdS/β-HgS nanoheterosystem are calculated and analyzed as functions of the geometric parameters of the quantum dot involved. It is demonstrated that an increase in the height of the quantum dot leads to a decrease in the energy of quasi-stationary exciton states of the Breit-Wigner type and to an increase in their lifetimes. The lifetime of exciton states is long enough for these states to be observed in the experiment. 相似文献
15.
A. O. Govorov K. Karrai R. J. Warburton A. V. Kalameitsev 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):295
We describe theoretically multiply-charged excitons interacting with a continuum of delocalized states. Such excitons exist in relatively shallow quantum dots and have been observed in recent optical experiments on InAs self-assembled dots. The interaction of an exciton and delocalized states occurs via Auger-like processes. To describe the optical spectra, we employ the Anderson-like Hamiltonian by including the interaction between the localized exciton and delocalized states of the wetting layer. In the absence of a magnetic field, the photoluminescence line shapes exhibit interference effects. When a magnetic field is applied, the photoluminescence spectrum demonstrates anticrossings with the Landau levels of the extended states. We show that the magnetic-field behavior of charged excitons is very different to that of diamagnetic excitons in three and two-dimensional systems. 相似文献
16.
We observed a quantum confinement effect in vertically well-aligned ultrafine ZnO nanorods using polarized excitation photoluminescence
measurements. Room-temperature and low-temperature photoluminescence spectra revealed that free excitons were confined in
the nanorods. The magnitude of the energy shift due to the quantum confinement in the ultrafine ZnO nanorods was 6 meV at
room temperature, which corresponded to the luminescence from ZnO nanorods 12.8 nm in diameter. The diameter estimated from
the spectra was comparable to the value measured from SEM images. 相似文献
17.
A. Babiński 《Opto-Electronics Review》2018,26(1):73-79
Properties of excitons confined to potential fluctuations due to indium distribution in the wetting layer which accompany self-assembled InAs/GaAs quantum dots are reviewed. Spectroscopic studies are summarized including time-resolved photoluminescence and corresponding single-photon emission correlation measurements. The identification of charge states of excitons is presented which is based on results of a theoretical analysis of interactions between the involved carriers. The effect of the dots’ environment on their optical spectra is also shown. 相似文献
18.
Low temperature emission spectra of localized excitons in CdS1?xSex solid solutions under the monochromatic excitation with tunable laser have been studied. It has been found that the luminescence of localized excitons has a high degree of linear polarization with respect to the polarization direction of exciting light. This polarization reflects the “hidden” anisotropy of macroscopically isotropic localized exciton system and strongly depends on the frequency of exciting light. Study of this dependence has permitted for the first time a determination of position of the “mobility edge” for exciton migration in disordered semiconductor solid solution. 相似文献
19.
The effect of a random field caused by impurities, interface roughness and so on, on the optical properties and superfluidity
of a quasi-two-dimensional system of excitons is studied. The influence of a random field on the density of the superfluid
component of excitonic systems at low temperatures is investigated. For quasi-two-dimensional excitonic systems in a random
field the Kosterlitz–Thouless temperature in the superfluid state is calculated. The superfluidity and Bose–Einstein condensation
of indirect excitons in coupled quantum dots are studied. Magnetoexciton light absorption in the disordered quantum wells
is considered. The two-particle problem of the magnetoexciton motion in the external field depending on the external magnetic
field is reduced to the one-particle motion with effective magnetic mass in some effective field. The energy and optical absorption
of the magnetoexciton in a single and coupled quantum dots are studied using the effective-magnetic-mass Hamiltonian. In the
coherent potential approximation the coefficient of magnetoexciton optical absorption in single and coupled quantum wells
is calculated. In the strong magnetic fields the exciton peak decreases with magnetic field increasing in accordance with
the experimental data. The localization of direct and indirect magnetoexcitons is investigated.
Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000 相似文献
20.
We calculated the photoluminescence spectra of charged magneto-excitons in single two-dimensional parabolic quantum dots, using an unrestricted Hartree–Fock method. The calculated luminescence spectra explain well the observed red shifts of transition energies of InAs/GaAs single quantum dot by additional electron capture in a dot. The magnetic-field-induced transition of the ground state configuration of trapped electrons causes drastic change in the photoluminescence spectra. The dependence of photoluminescence intensities of charged excitons on the excess energies of photogenerated carriers above the bulk GaAs energy gap is studied phenomenologically, by calculating the steady state electron population probability in a dot. 相似文献