共查询到20条相似文献,搜索用时 15 毫秒
1.
《Superlattices and Microstructures》1998,24(3):227-238
We have investigated the energy spectrum of a superlattice with wide quantum wells under the bias of an electric field perpendicular to the superlattice layers. By using photocurrent spectroscopy, transitions of Wannier–Stark levels for the various electron and hole states are observed, and at low fields, further structures corresponding to miniband edge transitions are found. Various anticrossings could be observed at higher and lower electric fields. The anticrossings at high electric fields are due to energy alignment of different electronic sublevels in adjacent wells. The anticrossing structures at low fields could be interpreted as resonances between intrawell and interwell excitonic Wannier–Stark states with equal sublevel states, where the anticrossing is caused by differences in exciton binding energy. Fitting of transitions and anticrossings was done by using a semi-empirical model and we have extracted relevant fitting parameters like the quantum-confined Stark coefficient, binding energies for the excitonic Wannier–Stark levels and the resonant coupling strength for states involved in the various anticrossing transitions. Finally, insight into the excitonic influences on the coupling of the WS states could be obtained by comparing the fitted parameters for the various transitions. 相似文献
2.
V. N. Grigor’ev O. V. Dorofeev K. L. Litvinenko V. G. Lysenko S. I. Onishchenko K. Leo B. Rosam K. Kohler 《Journal of Experimental and Theoretical Physics》2000,91(4):791-800
An investigation is made of the absorption spectra of a GaAs(82 Å)/Al0.07Ga0.93As(37 Å) superlattice at 10 K in electric fields between 0 and 60 kV/cm. By comparing the experimental absorption spectra with calculations of the energies and oscillator strengths of transitions between states of the Wannier-Stark ladder it is established that in strong electric fields above-barrier states do not form a structureless continuum but a fan of states. Intersection of electric-field-localized electron states with the fan of above-barrier states leads to broadening, splitting, and nonmonotonic changes in the intensity of an intrawell transition band. The additional absorption band observed can be attributed to intrawell transitions between states in the left and right quantum wells of the superlattice. 相似文献
3.
T. Imanishi M. Takeuchi K. Kawashima K. Fujiwara 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
Excitonic effects on Stark-ladder transitions have been investigated experimentally and theoretically in a novel asymmetric double-well superlattice consisting of wide and narrow GaAs quantum wells separated by a constant AlAs barrier. In this superlattice strong electron resonance can occur under the applied electric field between the wide and narrow wells. It is found that due to existence of the two different heavy-hole localized states two types of excitonic resonances which are staggered in field are observed in the low-temperature photocurrent spectra. This field difference in the staggered exciton resonances is rigorously explained by variational calculations of the changes in the direct and indirect exciton binding energies with the field. 相似文献
4.
Sang Chil Lee Hyung Soo Ahn Soon Hyun Kwon Suck Whan Kim 《Physica B: Condensed Matter》2012,407(17):3487-3492
A finite type-I superlattice with different dielectric media on either side of the surfaces is considered under a perturbing electric fields parallel to the superlattice axis on the basis of an infinite square potential well. Using the random-phase approximation, the density–density correlation function including intra- and inter-level transitions in a multiple-quantum-well (MQW) is calculated. The dispersion relations for the surface and the bulk states are obtained as functions of the momentum wave vector and the averaged electric field strength over the quantum well. The Raman intensities due to the bulk and the surface plasmons for the intra- and the inter-level transitions are also obtained for incoming light energy. 相似文献
5.
The absorption constant for intraband transitions in parabolic multiquantum well structures is calculated and compared with intraband absorption in a square well superlattice. The parabolic multiple quantum well structure may be used as an Infrared detector with the possibility of lower leakage current compared to one made of square wells. 相似文献
6.
I. M. Catalano A. Cingolani M. Lepore R. Cingolani K. Ploog 《Il Nuovo Cimento D》1990,12(10):1465-1474
Summary The two-photon absorption spectra of GaAs/AlGaAs multiple quantum well and superlattice structures have been experimentally
investigated by means of the nonlinear luminescence technique in different polarization configurations. A strong excitonic
effect overlapping the interband two-photon spectrum has been found and the selection rules for the excitonic transitions
have shown to greatly change for different polarizations. The comparison of linear and nonlinear absorption measurements provides
important information on the excited states of excitons in multiple quantum wells.
Work partially supported by M.P.I. 相似文献
7.
D. A. Firsov L. E. Vorobjev V. A. Shalygin V. Yu. Panevin A. N. Sofronov S. D. Ganichev S. N. Danilov A. V. Andrianov A. O. Zakhar’in A. E. Zhukov V. S. Mikhrin A. P. Vasil’ev 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(2):246-248
Spontaneous emission of terahertz radiation from structures with GaAs/AlGaAs quantum wells in a longitudinal magnetic field has been studied. It is shown that some bands in the emission spectrum can be related to radiative electron transitions between resonant and localized impurity states, as well as to the transitions with participation of subband states. The temperature dependence of the equilibrium intraband absorption of terahertz radiation and its modulation in a longitudinal electric field in GaAs/AlGaAs quantum wells has been investigated. 相似文献
8.
G. Bastard 《Superlattices and Microstructures》1985,1(3):265-273
We present the results of the calculations of some electronic properties of semiconductor quantum wells and superlattices. The review includes the superlattice band structure and the quantum well bound energy levels; the virtual bound states of semiconductor quantum wells and their influence on the energy spectrum of separate confinement heterostructures. Finally the perturbation of quantum well bound states and exciton states by a static electric field applied parallel to the growth axis is considered. 相似文献
9.
<正>According to the characteristic structure of double wells in bistable systems,this paper analyses stochastic fluctuations in the single potential well and probability transitions between the two potential wells and proposes a method of controlling stochastic resonance by using a periodic signal.Results of theoretical analysis and numerical simulation show that the phenomenon of stochastic resonance happens when the time scales of the periodic signal and the noise-induced probability transitions between the two potential wells achieve stochastic synchronization.By adding a bistable system with a controllable periodic signal,fluctuations in the single potential well can be effectively controlled,thus affecting the probability transitions between the two potential wells.In this way,an effective control can be achieved which allows one to either enhance or realize stochastic resonance. 相似文献
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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
13.
Starting from a model of an indirect optical semiconductor with two bands, the electron states are calculated in the presence of an additional periodic one-dimensional potential (superlattice) in the semiconductor material. These states are used to determine the transition probability connected with the absorption of a photon. This transition corresponds to an optical direct transition — no phonon takes part in this process. The optical direct and optical indirect transitions are compared. For optical frequencies near the band gap one expects only direct transitions, whereby the optical indirect transitions may be neglected. 相似文献
14.
N. V. Dyakonova O. A. Klimenko W. Knap Ya. A. Mityagin V. N. Murzin S. A. Savinov 《Bulletin of the Lebedev Physics Institute》2007,34(7):189-193
Long-wavelength IR radiation was detected in a long-period superlattice with wide quantum wells under conditions of electrical injection of charge carriers into lower size-quantization subbands, which was explained by intersubband transitions. The detected radiation probably suggests that there is a strongly nonequilibrium carrier distribution in subbands, caused by the difference between scattering processes into lower subbands with and without involving optical phonons. 相似文献
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A simple method to compute the carrier energy states, miniband parameters and dispersion characteristics for single and multiple quantum well and superlattice structures is presented. The method utilizes the continuity of the envelope function across the heterojunctions according to the boundary conditions that both the wavefunction ψ and the particle current density be continuous at each interface. The nonuniform potential distribution encountered in doped or compositionally graded materials is approximated by piecewise constant potential functions. In addition to being conceptually simple, the method is readily adopted to fairly complex structures where other more sophisticated methods such as LCAO, reduced Hamiltonian and tight binding theories may become unfeasible or unmanageable. It is shown that for an arbitrary stepped potential variation, the eigenvalues (or the energy states) of quantum wells or a finite number of coupled quantum wells can be found by utilizing a transverse resonance method which is readily implemented on a digital computer for the computation of these eigenvalues. For the case of periodic superlattices, the miniband parameters and the dispersion characteristics are computed from a suitably defined transmission matrix associated with a unit cell of the superlattice which may itself consist of multiple layers. Typical results for the computed parameters for several wells and simple, biperiodic, binary and polytype superlattices consisting of various AlxGa1?xAs and InxGa1?xAs alloys are presented. 相似文献
17.
Germano M. Penello Pedro H. Pereira Lesslie Guerra Luciana D. Pinto Roberto Jakomin Renato T. Mouro Marcos H. Degani Marcelo Z. Maialle Deborah Sivco Claire Gmachl Mauricio P. Pires Patricia L. Souza 《Annalen der Physik》2019,531(6)
Herein, two challenges are addressed, which quantum well infrared photodetectors (QWIPs), based on III‐V semiconductors, face, namely: photodetection within the so‐called “forbidden gap”, between 1.7 and 2.5 microns, and room temperature operation using thermal sources. First, to reach this forbidden wavelength range, a QWIP which consists of a superlattice structure with a central quantum well (QW) with a different thickness is presented. The different QW in the symmetric structure, which plays the role of a defect in the otherwise periodic structure, gives rise to localized states in the continuum. The proposed InGaAs/InAlAs superlattice QWIP detects radiation around 2.1 microns, beyond the materials bandoffset. Additionally, the wavefunction parity anomaly is explored to increase the oscillator strength of the optical transitions involving higher order states. Second, with the purpose of achieving room temperature operation, an asymmetric InGaAs/InAlAs superlattice, in which the QW with a different thickness is not in the center, is used to detect infrared radiation around 4 microns at 300 K. This structure operates in the photovoltaic mode because it gives rise to states in the continuum which are localized in one direction and extended in the other, leading to a preferential direction for current flow. 相似文献
18.
《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
19.
From the view of electron waving, taking account of the electron wave reflections at the interface between the well and the potential barrier layer we discuss the electronic states above the barriers in a GaAs/AlGaAs superlattice. We present a new method on calculating the breadth of the subband and the calculated breadth of GaAs/AlGaAs superlattice is in good agreement with experimental results. 相似文献
20.
The problem of the polaron spectrum is studied in a superlattice having narrow quantum wells and relatively wide potential barriers. A δ-like superlattice potential is chosen to solve the problem. This model is adequate, if the penetration depth of the electron wave function into the barrier region is much greater than the width of the quantum well. A weak-coupling polaron at low temperature is studied. Only volume phonons are considered. Expressions are obtained for the polaron mass and the shift of the polaron energy under these assumptions. To test the model, numerical calculations were performed for an InAs-GaSb superlattice, whose quantum wells are quite deep (the energy offset of the conduction bands in InAs and GaSb equals 830 meV), narrow (the width of a quantum well corresponds to the width of an InAs monolayer 6 Å), and the barrier width corresponding to the thickness of the GaSb layers equals 150 Å. The assumption that the penetration depth of the wave function is much greater than the barrier width holds well. 相似文献