共查询到20条相似文献,搜索用时 46 毫秒
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Karen J. Moore Geoffrey Duggan Age Raukema Karl Woodbridge 《Superlattices and Microstructures》1990,7(4)
Photoluminescence excitation (PLE) spectroscopy has been used to characterise miniband formation in (InGa)-As---GaAs superlattices with nominally 50 Å wide wells and barriers between 200 Å and 50 Å. The nominal composition of the alloy layers was 0.06. The observed exciton features are consistent with theoreical predictions of both parity allowed and forbidden transitions, at the mini-Brillouin zone centre and edge, including transitions associated with M1 critical points in the superlattice bandstructure. Furthermore, as the GaAs thickness is varied we monitor changes in shape of the PLE spectra in the region of the first free electron to heavy-hole subband continuum, brought about by the electron-hole Coulomb interaction within the miniband. We also report PLE measurements on a structure which has been designed specifically to maximise the possibility of revealing a Δn = 0 exciton resonance below the saddle point. 相似文献
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The dependence of infrared (IR) light absorption on external magnetic field is considered when the impurity level approaches the upper edge of spin-wave band of antiferromagnet. It is explained a strongly nonlinear field dependence and rapid decrease of corresponding line intensity been observed experimentally in Fe1?cCocF2. Such behaviour is due to existence of some subthreshold range near the band edge and corresponds to the incoherent collective rearrangement (ICR) of the system spectrum. 相似文献
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《Solid State Communications》1986,57(8):699-702
A k-space renormalization technique for evaluating the band structure of superlattices is examined. The large number of degrees of freedom of a superlattice tight-binding Hamiltonian is first reduced by exploiting the translational symmetry properties in layers perpendicular and parallel to the superlattice axis. The remaining degrees of freedom of the unit supercell are then systematically eliminated by renormalization techniques. Our combination of projective techniques on the one hand and full exploitation of symmetry properties on the other result in a very flexible and efficient algorithm. Some results for a simplified single-site model superlattice are presented as an example of our novel procedure. 相似文献
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The dc conductance, the universal quantum fluctuations and the resistance distribution are numerically investigated in dimer semiconductor superlattices by means of the transfer matrix formalism. We are interested in the GaAs/Alx Ga 1 − xAs layers, having identical thickness, where the aluminium concentration x takes, at random, two different values, with the constraint that one of them appears only in pairs, i.e. the random dimer barrier (RDB). These systems exhibit a miniband of extended states, around a critical energy, lying to the typical structure of the dimer cell. The states close to this resonant energy consist of weakly localized states, while in band tails i.e. for negligible conductance, the states are strongly localized. This is evidence of the suppression of localization in the RDB superlattices. The nature of the transition between these two regimes is quantitatively investigated through relevant physical quantities. The model is, hence, clearly and statistically examined. 相似文献
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L. A. Falkovsky E. G. Mishchenko 《Journal of Experimental and Theoretical Physics》2006,102(4):661-670
We theoretically consider a superlattice formed by thin conducting layers spatially separated between insulating layers. The
dispersion of two coupled phonon-plasmon modes of the system is analyzed by using the Maxwell equations, with the retardation
effect included. Both transmission for the finite plate and the absorption for the semi-infinite superlattice in the infrared
are calculated. Reflectance minima are determined by the longitudinal and transverse phonon frequencies in the insulating
layers and by the density-state singularities of the coupled modes. We also evaluate the Raman cross section from the semi-infinite
superlattice.
The text was submitted by the authors in English. 相似文献
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W. J. Hsueh C. H. Chen J. A. Lai 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(4):503-508
The splitting rules of fragmental miniband in Fibonacci superlattices (FSLs) with arbitrary basis and generation orders are
presented through a gap map diagram. Based on the gap map, we find the invariant conditions of the band structure splitting
in the FSL for arbitrary generation orders. Moreover, the band structure splitting can be divided to form many regions, each
having a similar pattern. In each region, the widths of most gap bands except two major gaps will decrease for increasing
the generation order. It is interesting that the center and gap width of the major gaps will converge to constant values for
increasing the generation order of the FSL. Based on the splitting rules displayed in the gap map, it is convenient to predict
the fragmental band structure in the FSL for arbitrary generation orders and bases. 相似文献
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K.K. Mon 《Solid State Communications》1982,41(9):699-700
We present the results of a theory of electronic energy bands of superlattices using an application of a recent novel empirical tight binding method. The theory is applied to GaAs-AlAs (001) superlattices with very good agreements with available experimental results for both the direct and indirect energy gaps. 相似文献
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It is shown that the rigid band model cannot be applied to the sodium tungsten bronzes outside of the cubic range. The origin of the band gap states observed in the semiconducting range is discussed. 相似文献
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《Journal of luminescence》1987,39(2):57-74
We have studied six GaAs/AlAs superlattices with periods ranging from 18 to 60 Å and different average aluminum composition. Three of these samples are shown to be direct bandgap materials whose band structure differs strongly from that of the corresponding alloy, but is correctly described by an envelope function calculation. The three remaining samples are shown to be indirect both in real and reciprocal space. The lowest energy transitions are found to arise from an exciton involving a heavy hole state mostly confined in the GaAs layer and at the Brillouin zone center (Λ), and an electronic state of X character confined in the AlAs layers. Analysis of the time decay of the luminescence shows that this is a momentum-forbidden exciton made allowed by disorder scattering, which leads to a luminescence efficiency comparable to that of the direct bandgap samples. Partial lifting of the degeneracy of the three X orbitals by the superlattice potential is also observed. Finally, we take advantage of the strong dependence of these indirect transition energies on the band discontinuities to estimate the valence band offset to be about 550 meV in this system. 相似文献
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M.A. Gilmore B.L. Johnson 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):297-305
We study the effects of layer thickness variations on the collective plasmon excitation modes of finite superlattices. Unlike
other symmetry lowering mechanisms, thickness variation does not strongly localize the surface modes. We find that the reason
for this insensitivity lies in the fact that the collective modes of a given finite structure must evolve continuously from
the single-finite-superlattice at zero thickness deviation into modes of a pair of uncoupled finite structures at large thickness
variation. We also show that this behavior is analogous to the evolution of molecular orbitals from atomic orbitals as the
internuclear separation is reduced, in contrast to the analogy of the superlattice modes as a stack of coupled quantum wells.
This emphasizes the difference between the electromagnetic symmetry of the finite superlattice and the structural symmetry.
Received 16 April 2001 and Received in final form 6 July 2001 相似文献