共查询到20条相似文献,搜索用时 15 毫秒
1.
The energy of a biexciton in a GaAs/AlxGa1?xAs quantum well structure with finite barriers is investigated by using the geometrical model of two-dimensional biexcitons proposed by Singh et al. [J. Singh, D. Birkedal, V.G. Layssenko, J.M. Hvam, Phys. Rev. B 53 (1996) 15909; I.-K. Oh, J. Singh, Phys. Rev. B 60 (1999) 2528]. A fractional-dimensional approach is used to obtain the binding energy of the biexciton in both square quantum wells and parabolic quantum wells. Theoretical results show that the binding energy of a biexciton in a finite quantum well exhibits a maximum with increasing well width. The ratio of the binding energy of a biexciton to that of an exciton in a quantum well structure is found to be sensitive to the electron-to-hole mass ratio and larger than that in the three-dimensional system. The results agree fairly well with previous experimental results. The results of our approach are also compared with those of earlier theories. 相似文献
2.
A GaAs/Al x Ga1? x As semiconductor structure is proposed, which is predicted to superconduct at T c?≈?2?K. Formation of an alternating sequence of electron- and hole-populated quantum wells (an electron–hole superlattice) in a modulation-doped GaAs/Al x Ga1? x As superlattice is considered. This superlattice may be analogous to the layered electronic structure of high-T c superconductors. In the structures of interest, the mean spacing between nearest electron (or hole) wells is the same as the mean distance between the electrons (or holes) in any given well. This geometrical relationship mimics a prominent property of optimally doped high-T c superconductors. Band bending by built-in electric fields from ionized donors and acceptors induces electron and heavy-hole bound states in alternate GaAs quantum wells. A proposed superlattice structure meeting this criterion for superconductivity is studied by self-consistent numerical simulation. 相似文献
3.
B. A. Aronzon A. S. Lagutin V. V. Ryl’kov V. V. Tugushev V. N. Men’shov A. V. Lashkul R. Laiho O. V. Vikhrova Yu. A. Danilov B. N. Zvonkov 《JETP Letters》2008,87(3):164-169
The field and temperature dependences of the magnetization of GaAs/δ〈Mn〉/GaAs/In x Ga1 ? x As/GaAs quantum wells with the δ〈Mn〉 layer separated from the well by a 3-nm GaAs spacer have been studied in the temperature range of 3–300 K in a magnetic field up to 6 T. An external magnetic-field-induced phase transition to a ferromagnetic state with a magnetization hysteresis loop shifted from a zero magnetic field has been found to occur at a temperature below 40 K. A theoretical model is proposed that implies the coexistence of ferromagnetically and antiferromagnetically ordered regions within the GaAs layers. 相似文献
4.
A. Hospodková E. Hulicius J. Oswald J. Pangrác K. Melichar T. Šimeček 《Czechoslovak Journal of Physics》1999,49(5):805-811
Luminescence properties of strained In
x
Ga1−x
As/GaAs multiple quantum wells of different thickness and In content, prepared by metal organic vapour phase epitaxy were
studied. The influence of the quantum well material composition on the shape of luminescence spectra was investigated. The
experimental results were fitted by the Model Solid Theory. This fit was improved by the use of adjustedQ parameter.
Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17,
1998.
This work was supported by Grant Agency of Czech Republic under grants numbers 202/98/0074, 102/99/0414 and Grant Agency of
Academy of Sciences No. A 10110807/1998. 相似文献
5.
《Superlattices and Microstructures》1988,4(2):141-145
We present a magneto-optical study of p-type GaAs/AlxGa1−xAs quantum wells doped with Be acceptors over the central one-third of the GaAs layers. Using magneto-reflectance and magneto-luminescence spectroscopies, we have investigated (a) interband Landau transitions and (b) transitions from the conduction band Landau levels to the Be acceptors. Binding energies of the acceptors were determined and the dependence of the impurity ground state energy on magnetic field has been studied. 相似文献
6.
《Superlattices and Microstructures》1998,23(2):289-296
In order to investigate the symmetry (i.e. sphericity) of donor–bound electron wavefunctions in quantum wells, we have invoked a two-parameter trial wavefunction. One parameter is the Bohr radius λ, whilst the other is the eccentricity parameter ζ. The latter incorporates the effect of the quantum well (QW) on the carrier motion in the growth (i.e. the z) direction. Working within the envelope function approximation it is shown that the donor wavefunction has the form of a prolate spheroid. However, calculations of the ratio λ/ζ shows that it is the value of λ which determines the essential symmetry of the wavefunction. 相似文献
7.
《Superlattices and Microstructures》1987,3(3):251-256
Recent research of superlattices and multiple quantum wells has generated considerable interest in the optical waveguiding properties of these structures for optoelectronic applications. As a result we present a theoretical study of the index of refraction of superlattices and determine its variation as a function of frequency and the superlattice parameters, i.e., layer width and AlAs composition. Γ-region exciton and valence-band mixing effects are included in the model. It is found that these two effects have an important influence on the value of the index of refraction and that superstructure effects rapidly decrease for energies greater than the superlattice potential barriers. Because of the quasi-two-dimensional character of the Γ-region excitons, our results indicate that the superlattice index of refraction can vary by ∼ 2% at the quantized, bound-exciton, transition energies. Overall, the theoretical results are in good agreement with the experimental data. 相似文献
8.
I. G. Aksyanov A. V. Kudinov Yu. G. Kusraev B. P. Zakharchenya T. Wojtowicz G. Karczewski J. Kossut 《Physics of the Solid State》1999,41(5):820-823
A study is reported of the anisotropy in magnetic-field-induced linear polarization in (001) CdTe/Cd1−x
MnxTe quantum wells. The observed limiting anisotropy is shown to be due to the low C
2v
symmetry of the quantum well. The relations obtained for the C
2v
point group are in a good agreement with experiment. Considered on the microscopic scale, the effect is associated with the
heavy-hole g-factor anisotropy in the well plane.
Fiz. Tverd. Tela (St. Petersburg) 41, 903–906 (May 1999) 相似文献
9.
10.
This paper studies the dynamics of intra-acceptor hole relaxation in
Be δ -doped GaAs/AlAs multiple quantum wells (MQW) with
doping at the centre by time-resolved pump-probe spectroscopy using
a picosecond free electron laser for infrared experiments. Low
temperature far-infrared absorption measurements clearly show three
principal absorption lines due to transitions of the Be acceptor from
the ground state to the first three odd-parity excited states
respectively. The pump-probe experiments are performed at different
temperatures and different pump pulse wavelengths. The hole
relaxation time from 2p excited state to 1s ground state in MQW is
found to be much shorter than that in bulk GaAs, and shown to be
independent of temperature but strongly dependent on wavelength. The
zone-folded acoustic phonon emission and slower decay of the
wavefunctions of impurity states are suggested to account for the
reduction of the 2p excited state lifetime in MQW. The wavelength
dependence of the 2p lifetime is attributed to the diffusion of the
Be atom δ -layer in quantum wells. 相似文献
11.
L. V. Butov A. V. Mintsev A. I. Filin K. Eberl 《Journal of Experimental and Theoretical Physics》1999,88(5):1036-1044
The kinetics of indirect photoluminescence of GaAs/AlxGa1−x
As double quantum wells, characterized by a random potential with a large amplitude (the linewidth of the indirect photoluminescence
is comparable to the binding energy of an indirect exciton) in magnetic fields B≤12 T at low temperatures T≥1.3 K is investigated. It is found that the indirect-recombination time increases with the magnetic field and decreases with
increasing temperature. It is shown that the kinetics of indirect photoluminescence corresponds to single-exciton recombination
in the presence of a random potential in the plane of the double quantum wells. The variation of the nonradiative recombination
time is discussed in terms of the variation of the transport of indirect excitons to nonradiative recombination centers, and
the variation of the radiative recombination time is discussed in terms of the variation of the population of optically active
excitonic states and the localization radius of indirect excitons. The photoluminescence kinetics of indirect excitons, which
is observed in the studied GaAs/AlxGa1−x
As double quantum wells for which the random potential has a large amplitude, is qualitatively different from the photoluminescence
kinetics of indirect excitons in AlAs/GaAs wells and GaAs/AlxGa1−x
As double quantum wells with a random potential having a small amplitude. The temporal evolution of the photoluminescence
spectra in the direct and indirect regimes is studied. It is shown that the evolution of the photoluminescence spectra corresponds
to excitonic recombination in a random potential.
Zh. éksp. Teor. Fiz. 115, 1890–1905 (May 1999) 相似文献
12.
The effect of n doping on the band structure of lattice-matched GaNAsBi/GaAs quantum wells was investigated using a self-consistent calculation combined with the 16-band anti-crossing model. Bi/N incorporation and doping effects can offer a huge potential to engineer the electronic band structure of such materials suitable for the design of photodetectors and emitters operating at 1.3 µm. The increase of the doping density induces a blue-shift of the fundamental transition energy in the doping range between 6×1017 and 5×1018 cm−3. The absorption spectra dependence on the well width are discussed. To maintain the fundamental transition fixed at the wavelength 1.3 µm, we have adjusted the Bi composition for the well width range between 4.5 and 10 nm with respect of the confinement conditions. 相似文献
13.
《Solid State Communications》1986,60(8):669-673
The results of direct measurements of the diamagnetic shift of axciton levels in narrow quantum wells of a thickness varying between 25 and 150 Å are reported. A perturbation type approach is used to calculate the diamagnetic shift of 1s exciton levels in quantum well structures of Ga1−xAlxAs-GaAs-Ga1−xAlxAs. The calculations are applicable in the weak field range for which the Coulomb energy dominates over the magnetic one. The experimental results are in satisfactory agreement with the theory throughout the entire well thicknesses range. 相似文献
14.
B. A. Aronzon A. B. Granovsky A. B. Davydov Yu. A. Danilov B. N. Zvonkov V. V. Ryl’kov E. A. Uskova 《Physics of the Solid State》2007,49(1):171-177
A method of formation of two-dimensional structures containing a δ〈Mn〉-doped layer in GaAs and an InxGa1?x As quantum well (QW) separated by a GaAs spacer of thickness d = 4–6 nm is developed using laser evaporation of a metallic target during MOS hydride epitaxy. It is shown that, up to room temperature, these structures have ferromagnetic properties most likely caused by MnAs clusters. At low temperatures (T m ~ 30 K), the anomalous Hall effect is revealed to occur. This effect is related to hole scattering by Mn ions in GaAs and to the magnetic exchange between these ions and QW holes, which determines the spin polarization of the holes. The behavior of the negative magnetoresistance of these structures at low temperatures indicates the key role of quantum interference effects. 相似文献
15.
《Superlattices and Microstructures》2001,29(3):225-231
The temperature dependence of excitonic transitions in double quantum well heterostructures in the temperature range of 2–300 K were investigated. A crossing between excitonic transition experimental curves as a function of temperature in quantum wells of the same thickness and different barrier height is observed. The influence of the barrier height on the temperature dependence of excitonic states in the quantum wells is analyzed. 相似文献
16.
《Superlattices and Microstructures》1997,22(3):263-271
Well-width dependence of quantum and transport mobilities of electrons in GaAs/GaAlAs multiple quantum wells is studied for wells with widths ranging between 50 Å and 145 Å Experimental results are obtained from the amplitude analysis of the Shubnikov–de Haas (SdH) oscillations and from conventional Hall measurements at temperatures betweenT = 15 K and 4.2 K. A novel technique is employed to estimate, theoretically, the interface roughness parameters from electron quantum and transport lifetimes. The modelling is carried out for a range of layer fluctuations, width (Δ) and lateral size (Λ), as to obtain the best fit to the experimental results for individual samples. Our results indicate that the interface roughness scattering limits equal both quantum and transport mobilities at low temperatures, and that the nature of scattering by interface roughness (small or large angle) depends not only on the size and the width of the fluctuations but also on the distribution of these fluctuations within the samples. Therefore, unlike the predictions of the existing theoretical models, which assume constant values of Δ and Λ for all well widths, the well-width dependence of interface roughness scattering cannot be verified experimentally. 相似文献
17.
Tunneling-induced π-phase shift with a single-photon signal field in asymmetric double quantum wells
A theoretical investigation is carried out into the cross phase modulation (XPM) in an asymmetric double A1GaAs/GaAs quantum wells structure with a common continuum. It is found that, combining resonant tunneling-induced transparency and constructive interference in the third-order Kerr effect, a giant XPM can be achieved with vanishing linear and nonlinear absorptions, accompanied by the velocities of the probe and signal fields being matched. Furthermore, this giant XPM could induce a π-phase shift at a single-photon level which is favorable for the applications in two-qubit quantum logic gates. 相似文献
18.
19.
20.
Two metastable states of a multilayer Ge/p-Ge1−x
Six heterosystem with wide (∼ 35 nm) potential wells (Ge) are observed in strong magnetic fields B at low temperatures. In the first state, the Hall resistivity exhibits an inflection near the value ρxy=h/e
2 scaled to one Ge layer. The longitudinal magnetoresistivity ρxx(B) possesses a minimum in the range of fields where this inflection occurs. The temperature evolution of the inflection in
ρxy(B), the minimum of ρ xx(B), and the value of ρxy at the inflection indicates a weakly expressed state of the quantum Hall effect with a uniform current distribution over
the layers. In the second metastable state, an unusually wide plateau near h/2e
2 with a very weak field dependence is observed in ρxy(B). Estimates show that in these samples the Fermi level lies below but close to the top of the inflection in the bottom of
the well. For this reason, the second state can be explained by separation of a hole gas in the Ge layers into two sublayers,
and the saturation of ρxy(B) near h/2e
2 can be explained by the formation of a quantum Hall insulator state.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 290–297 (25 August 1999) 相似文献