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1.
《Superlattices and Microstructures》1987,3(5):471-475
The optical properties of GainAsInP quantum wells are studied in magnetic fields of up to 16T. A comparison of the absorption and photoluminescence spectra of a series of multiple quantum wells provides evidence that the photoluminescence occurs from excitons in which the hole is localised. This localisation is shown to be present in a highly doped sample with a sheet carrier density of ∼1012 cm−2, indicating that the localisation is not screened out by high free carrier densities. A theoretical fit to measured Landau level transitions in a 100Å multiple quantum well allows values for the carrier masses, electron non-parabolicity and exciton binding energy to be determined. 相似文献
2.
《中国光学快报(英文版)》2008,(9)
We investigate intersubband Rabi flopping in modulation-doped semiconductor quantum wells with and without the propagation effects,respectively.It is shown that propagation effects have a larger impact on Rabi flopping than the nonlinearities rooted from electron-electron interactions in multiple quantum wells. By using ultrashortπpulses,an almost complete population inversion exists if the propagation effects are not considered;while no complete population inversion occurs in the presence of propagation effects. Furthermore,the magnitude of the impact of propagation effects may be controlled by varying the carrier density. 相似文献
3.
《Superlattices and Microstructures》1988,4(3):359-361
By studying the temperature dependence of absorption and luminescence in modulation doped GaAsAlGaAs quantum wells, we show experimentally that the lowest energy absorption peak has a behavior strikingly different from the corresponding excitonic peak in undoped quantum wells, which is alos unexpected in the frame of the single particle picture. We find good qualitative agreement with the many-body model that attributes this “correlation singularity” to the interaction between the photoexcited hole and the sea of electrons. 相似文献
4.
5.
《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
6.
《Superlattices and Microstructures》1988,4(2):207-211
We have studied the perpendicular transport in the double-barrier structures of the InGaAs system, with particular focus on reducing the large leakage current caused by conduction at the perimeter of the device. Results obtained on a sample which had low doping in the electrode layers, such that the Fermi level of the emitter electrode was below the first subband level at low bias, are presented. These results demonstrate unambiguously that the process of selectively etching the device has been successful in suppressing the leakage current. A peak-to-valley ratio of 4.3 was obtained for this sample at 4.2K. We have also carried out the first investigation of the perpendicular transport in InGaAs superlattice structures. These structures exhibit a large series of periodic negative differential resistance whose number and period are controlled by the number of the width of the quantum wells respectively. 相似文献
7.
《Superlattices and Microstructures》1986,2(3):247-250
Employing temperature dependent photoconductivity, photoluminescence and photoreflectivity measurements, we have analyzed a GaAsAlAs multiple quantum well. The above optical techniques clearly resolve the fundamental inter-subband transitions, including heavy hole-light hole splittings. At T < 60K an anomalously high photoconductivity was discovered below the direct inter-subband transitions and is attributed to the presence of interface states. For T ≥ 100K the fundamental indirect Λ - J transition was discovered and associated with L0 (L) - phonon absorption. The energetic positions of the direct and the indirect gaps are in agreement with previous band structure calculations for GaAs/AlAs superlattices. 相似文献
8.
《Superlattices and Microstructures》1988,4(2):237-241
We have studied the temperature dependence of migration of atoms on growth-interrupted and uninterrupted GaAs and AlAs growth front in molecular beam epitaxy. The optimum growth condition for achieving truly-smooth surface on an atomic scale is found to be quite different between GaAs and AlAs. On this basis, we have developed a novel temperature-switched technique by which both top (AlAs-on-GaAs) and bottom (GaAs-on-AlAs) interfaces in GaAsAlAs quantum wells can be prepared truly-smooth. 相似文献
9.
《Superlattices and Microstructures》1998,23(5):1015-1018
The electron energy levels in doped nonabrupt GaAs/AlxGa1 − xAs single quantum wells 100 Å wide are calculated. Interface widths varying from zero to four GaAs unit cells are taken into account, as well as band bendings of 0–90 meV. It is shown that interface effects on the energy levels are important and sensitive to the level of doping. When interfaces of only two GaAs unit cells and a band bending of 40 meV are considered, the ground-state (first excited state) energy level shifts toward energies as high as 4 meV (20 meV). 相似文献
10.
V. P. Martovitsky V. I. Kozlovsky P. I. Kuznetsov D. A. Sannikov 《Journal of Experimental and Theoretical Physics》2007,105(6):1209-1221
An X-ray diffraction method that uses a slightly diverging (3′) beam and maximally attainable diffraction angles ? B (as large as 77°) was developed to study quantum wells (QWs) with widths of 5–8 nm separated by wide (100–220 nm) barrier layers. The advantage of this method compared to the use of a parallel beam is an increase by two orders of magnitude in the intensity of the beam incident on the sample and an increase in the probability of diffraction for all QWs as a unified single crystal. It is found that the growth on GaAs substrates misoriented by 10° from the (001) plane in the [111]II direction brings about monoclinization of crystal lattices of the QW layers and barrier layers in opposite directions. Inhomogeneity of composition over the thickness of each well is observed. In the case of growth of a ZnSe/ZnMgSSe structure in which the layers have a crystal-lattice period close to the lattice period of the GaAs substrate, the QWs are inhomogeneously doped with elements from the composition of the barrier layers. The inhomogeneity of QW composition observed in the growth of mismatched layers in ZnCdSe/ZnSSe and ZnCdS/ZnSSe structures is caused by the fact that mismatch between the lattice parameters of QWs and barriers stimulates the growth of self-consistent compositions; this occurs due to a decrease in the Cd concentration in the Zn1?x Cd x Se QW in the initial stages of growth compared to the Cd concentration in the flow of gases and an increase in the Zn concentration in the Cd1?x Zn x S QW at small values of x up to the concentration matching GaAs (x = 0.4). The mismatch stresses are partially relaxed via dislocations with the (111)II glide planes, as a result of which is observed the combination of rotation of the crystal planes of the layers and QW around the [1\(\overline 1 \)0] axis and almost cylindrical bending of the entire sample around the perpendicular [110] axis. Mismatch between lattice parameters of the ZnMgSSe barrier layers and the substrate brings about decomposition of these layers into two phases; this decomposition is caused by thermodynamic instability of the alloy. 相似文献
11.
In this paper we review the radiative recombination processes occurring in semiconductor quantum wells and superlattices under different excitation conditions. We consider processes whose radiative efficiency depends on the photogenerated density of elementary excitations and on the frequency of the exciting field, including luminescence induced by multiphoton absorption, exciton and biexciton radiative decay, luminescence arising from inelastic excitonic scattering, and electron-hole plasma recombination. Semiconductor quantum wells are ideal systems for the investigation of radiative recombination processes at different carrier densities owing to the peculiar wavefunction confinement which enhances the optical non-linearities and the bistable behaviour of the crystal. Radiative recombination processes induced by multi-photon absorption processes can be studied by exciting the crystal in the transparency region under an intense photon flux. The application of this non-linear spectroscopy gives direct access to the excited excitonic states in the quantum wells owing to the symmetry properties and the selection rules for artificially layered semiconductor heterostructures. Different radiative recombination processes can be selectively tuned at exciting photon energies resonant with real states or in the continuum of the conduction band depending on the actual density of photogenerated carriers. We define three density regimes in which different quasi-particles are responsible for the dominant radiative recombination mechanisms of the crystal: (i) The dilute boson gas regime, in which exciton density is lower than 1010 cm-2. Under this condition the decay of free and bound excitons is the main radiative recombination channel in the crystal. (ii) The intermediate density range (n < 1011 cm-2) at which excitonic molecules (biexcitons) and inelastic excitonic scattering processes contribute with additional decay mechanisms to the characteristic luminescence spectra. (iii) The high density range (n ?1012 cm-2) where screening of the Coulomb interaction leads to exciton ionization. The optical transitions hence originate from the radiative decay of free-carriers in a dense electron-hole plasma. The fundamental theoretical and experimental aspects of the radiative recombination processes are discussed with special attention to the GaAs/Al x Ga1-x As and Ga x In1-x As/Al y In1-y As materials systems. The experimental investigations of these effects are performed in the limit of intense exciting fields by tuning the density of photogenerated quasi-particles and the frequency of the exciting photons. Under these conditions the optical response of the quantum well strongly deviates from the well-known linear excitonic behaviour. The optical properties of the crystal are then no longer controlled by the transverse dielectric constant or by the first-order dielectric susceptibility. They are strongly affected by many-body interactions between the different species of photogenerated quasi-particles, resulting in dramatic changes of the emission properties of the semiconductor. The systematic investigation of these radiative recombination processes allows us to selectively monitor the many-body induced changes in the linear and non-linear optical transitions involving quantized states of the quantum wells. The importance of these effects, belonging to the physics of highly excited semiconductors, lies in the possibility of achieving population inversion of states associated with different radiative recombination channels and strong optical non-linearities causing laser action and bistable behaviour of two-dimensional heterostructures, respectively. 相似文献
12.
《Superlattices and Microstructures》1998,24(2):143-147
We present low temperature photoluminescence spectra taken from an 11Å ZnSe quantum well in ZnS barriers. The samples are grown by the technique of photo-assisted vapour phase epitaxy (PAVPE) and the spectra show evidence for interface disorder. The observed dependences of the excitonic luminescence on excitation power and temperature are interpreted by a model involving excitonic localization below an exciton mobility edge. This mobility edge is measured for these samples to be 6 meV below the free exciton energy in the ideal quantum well. 相似文献
13.
We investigate the transport scattering time, the single-particle relaxation time and the magnetoresistance of a quasi-two-dimensional electron gas in a GaP/AlP/GaP quantum well at zero and finite temperatures. We consider the interface-roughness and impurity scattering, and study the dependence of the mobility, scattering time and magnetoresistance on the carrier density, temperature and local-field correction. In the case of zero temperature and Hubbard local-field correction our results reduce to those of Gold and Marty (Physica E 40 (2008) 2028; Phys. Rev. B 76 (2007) 165309). We also discuss the possibility of a metal–insulator transition which might happen at low density. 相似文献
14.
《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
15.
《Superlattices and Microstructures》1999,26(4):263-277
Within the framework of a simple envelope function and effective mass approximation, by including the spatial variation of effective mass and nonparabolicity effects, we have investigated the energy spectrum and intersubband optical absorption in a quantum well with additional thin and higher (δ -like) cladding barriers on either side of the well. The dependence of the absorption coefficient on the structure parameters, doping level, photon energy and temperature has been investigated. The absorption coefficient and spectrum strongly depend on the cladding barrier tunnel transparency. The peak absorption wavelength is shifted towards the high energies as the barrier transparency decreases. The temperature shift of the absorption peak is very small. The results are compared with experiments of Schneider et al. taking into account the broadening induced by well width fluctuations. 相似文献
16.
Humberto Noverola-Gamas Luis Manuel Gaggero-Sager and Outmane Oubram 《中国物理 B》2022,31(4):44203-044203
The effects of the interlayer distance on the nonlinear optical properties of n-type quadruple δ-doped GaAs quantum well were theoretically investigated. Particularly, the absorption coefficient and the relative refraction index change were determined. In the effective mass approach and within the framework of the Thomas-Fermi theory, the Schrödinger equation was resolved. Thereby, the subband energy levels and their respective wave functions were calculated. The variations in the nonlinear optical properties were determined by using the density matrix solutions. The achieved results demonstrate that the interlayer distance causes optical red-shift on nonlinear optical properties. Therefore, it can be deduced that the suitably chosen interlayer distance can be used to tune optical properties within the infrared spectrum region in optoelectronic devices such as far-infrared photo-detectors, high-speed electronic-optical modulators, and infrared lasers. 相似文献
17.
18.
Rong Lü Hui Hu Jia-Lin Zhu Xiao-Bing Wang Lee Chang Bing-Lin Gu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):349-361
Resonant quantum tunneling of the Néel vector between nonequivalent magnetic wells is investigated theoretically for a nanometer-scale
single-domain antiferromagnet with biaxial crystal symmetry in the presence of an external magnetic field applied along the
easy anisotropy axis, based on the two-sublattice model. Both the Wentzel-Kramers-Brillouin exponent and the preexponential
factors are evaluated in the instanton contribution to the tunneling rate for finite and zero magnetic fields by applying
the instanton technique in the spin-coherent-state path-integral representation, respectively. The quantum interference or
spin-parity effects induced by the topological phase term in the Euclidean action are discussed in the rate of quantum tunneling
of the Néel vector. In the absence of an external applied magnetic field, the effect of destructive phase interference or
topological quenching on resonant quantum tunneling of the Néel vector is evident for the half-integer excess spin antiferromagnetic
nanoparticle. In the weak field limit, the tunneling rates are found to oscillate with the external applied magnetic field
for both integer and half-integer excess spins. We discuss the experimental condition on the applied magnetic field which
may allow one to observe the topological quenching effect for nanometer-scale single-domain antiferromagnets with half-integer
excess spins. Tunneling behavior in resonant quantum tunneling of the magnetization vector between nonequivalent magnetic
wells is also studied for a nanometer-scale single-domain ferromagnet by applying the similar technique, but in the large
noncompensation limit.
Received 4 June 1999 相似文献
19.
E. A. Mulyarov N. N. Sibel’din M. L. Skorikov V. A. Tsvetkov B. Etienne 《JETP Letters》1999,70(9):621-627
Lines corresponding to localized excitonic states formed from “above-barrier” electron and/or hole states (specifically, excitation
lines of excitons formed by an electron localized in a QW and a free heavy hole) have been observed in the photoluminescence
excitation spectra of GaAs/Al0.05Ga0.95As structures with quantum wells (QWs), each containing one single-particle size-quantization level for charge carriers of
each type. A computational method is proposed that permits finding the binding energy and wave functions of excitons in QWs
taking the Coulomb potential into account self-consistently. The computed values of the excitonic transition energies agree
quite well with the experimental results.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 9, 613–619 (10 November 1999) 相似文献
20.
μ+SR in magnetically ordered BCC metals: Local fields, μ+ sites,quantum diffusion,and strain effects
The paper gives a critical discussion of the procedures for extracting from the
+SR signals obtainable on magnetically ordered metals information on
+ sites, on local lattice distortions induced by the
+, on the local magnetic fields felt by the
+, and on quantum diffusion. Results for-Fe are:
+ occupy O sites, the tetragonality of the elastic double-force tensor isA–B 2eV, the dipolar magnetic field acting on the
+ isB
dip=(0.66±0.02)T. Using this information
+ hopping rates and diffusivities in Fe are deduced and compared with diffusivities obtained for hydrogen and deuterium. From this it is concluded that hydrogen in Fe diffuses via the adiabatic mechanism. In addition, the paper contains a brief summary of the theoretical background required for taking advantage of the rather large ¦A– B¦ values expected for
+ at O sites in bcc metals in order to gain information on the effects of energy asymmetries between neighbouring
+ sites on the + hopping rates. 相似文献