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1.
The quasi-bound states of electrons and holes in coupled GaAsAlGaAs quantum wells in the presence of an applied electric field perpendicular to the wells are determined by the exact solution of the Schroedinger equation using the iteration matrix formalism. The transmission probability in a finite superlattice is also calculated taking into account the exact wave functions in the barriers and wells. The method can be useful to interpret recent tunneling-current measurements.  相似文献   

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The density of states function for continuum states in the presence of a nuclear Coulomb field is derived by the Sommerfeld-Weyl eigendifferential method.  相似文献   

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n维相对论粒子的量子态密度及其应用   总被引:2,自引:0,他引:2  
利用半经典近似的方法,推导出了n维相对论自由粒子量子态密度以及黑体辐射中两类粒子的辐射公式的统一表达式,并且给出了低维情况下的表达式,所得结果与三维空间的预期结果一致.这对于深化低维体系的教学与研究具有重要的意义.  相似文献   

4.
We have investigated the influence of the final states of bound-to-continuum transitions within the conduction band of asymmetric quantum well structures on the photocurrent. This influence manifests itself by an energy-dependent oscillation of the current direction. We observe pronounced oscillations at zero bias voltage in a double quantum well structure, induced by an asymmetric excitation into continuum states with positive and negative momentum, i.e. by a photogalvanic effect (PGE). If this effect is superimposed on an asymmetric backrelaxation, similar oscillations are observed in the spectrum when the latter asymmetry is compensated by an external electric field. Theoretically, we find a strong relation between the PGE and a quantum interference effect occurring in the continuum.  相似文献   

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The sequential excited-to-excited state resonant tunneling effect was observed in weakly coupled long-period superlattices resulting in additional negative differential conductivity resonances in multistable current–voltage characteristics. The results obtained show the evidence of the highly nonequilibrium distribution of carriers over subbands with energies below the optical phonon energy in superlattices. A new type of electric field domains, due to resonant tunneling between excited subbands in adjacent wells, is considered, and experimental evidencies of such a domain's existence are given.  相似文献   

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A new method for the derivation of the density of final states in the nuclear equilibration process, based on the Darwin-Fowler method of statistical physics, is suggested. This method is generally valid for an arbitrary energy level scheme and includes the Pauli principle. When it is applied to the equidistant-spacing energy level scheme, the results are very close to those derived by Oblo?inský et al.  相似文献   

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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   

10.
Birkedal  D.  Sayed  K. E.  Sanders  G.  Lyssenko  V. G.  Stanton  C.  Hvam  J. M. 《Il Nuovo Cimento D》1995,17(11):1359-1366
Il Nuovo Cimento D - The optical properties of multiple quantum wells in the transition from isolated wells to a superlattice are investigated theoretically and experimentally. For superlattices...  相似文献   

11.
We characterize equilibrium states of quantum systems by a condition of passivity suggested by the second principle of thermodynamics. Ground states and -KMS states for all inverse temperatures 0 are completely passive. We prove that these states are the only completely passive ones. For the special case of states describing pure phases, assuming the passivity we reproduce the results of Haag et al.  相似文献   

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An interesting property of modulated semiconductor materials is that their reflectance and absorption spectra can nearly be chosen at will by adjusting the layer geometry. Introducing the concept of phonon-polariton density of states, this paper is aimed at investigating spectral properties of multilayered materials in the infra-red frequency range. Using powerful analytical methods, we will successively consider the cases of infinite and semi-infinite superlattices. The local density of states of polariton modes is obtained using a Green's function technique. Complete information is then available on allowed radiative and non-radiative electromagnetic excitations, (as a function of frequency and wavelength), at any depth in the stratified material. This approach will depict the essential role played by the surface, which changes significantly the polariton density of states as compared to ideal unbounded materials. In multilayered materials, in addition to the effect induced by the surface, one can similarly investigate the influence of the internal interfaces on the polariton local density of states and, from these, on the optical properties of those systems. Electromagnetic eigenmodes arising from the accumulation of interfaces are crucial to assess the spectral properties involving TM-polarized radiations. Effects related to the TE-polarized radiations are explained from the macroscopic anisotropy due to the alternate growth of different semiconductors. These results will be used to discuss reflectance experiments and simulated ATR spectra.  相似文献   

14.
The semiclassical motion of an electron along the axis of a superlattice may be calculated from the miniband dispersion curve. Under a weak electric field the electron executes Bloch oscillations which confines the motion along the superlattice axis. When a magnetic field, tilted with respect to the superlattice axis, is applied the electron orbits become chaotic. The onset of chaos is characterised by a complex mixed stable-chaotic phase space and an extension of the orbital trajectories along the superlattice axis. This delocalisation of the orbits is also reflected in the quantum eigenstates of the system some of which show well-defined patterns of high probability density whose shapes resemble certain semiclassical orbits. This suggests that the onset of chaos will be manifest in electron transport through a finite superlattice. We also propose that these phenomena may be observable in the motion of trapped ultra-cold atoms in an optically induced superlattice potential and magnetic quadrupole potential whose axis is tilted relative to the superlattice axis.  相似文献   

15.
We study the energy spectrum of the impurity states in tunnel-coupled double quantum wells for Coulomb and short-range donor potentials. We calculate the impurity contribution and the density of states and detect the transformation of a localized donor state into a resonant state when the binding energy of the donor in an isolated quantum well is less than the separation of the energy levels of the double quantum wells. In the opposite case, where the binding energy is greater than the level separation, there is tunneling repulsion between adjacent impurity levels, with the degree of degeneracy of the levels changing when there is tunneling mixing of the ground and excited impurity states from different wells. Resonant states emerge in an asymmetric double quantum well, while in a symmetric double quantum well the impurity level at the barrier’s center proves to be localized even against the background of the continuum. The calculations are based on a general expression for the impurity contribution to the density of states in terms of a 2-by-2 matrix Green’s function, i.e., only a pair of tunnel-coupled levels of the double quantum wells is taken into account. For an impurity with a short-range potential, we derive a matrix generalization of the Koster-Slater solution, while the impurity with a Coulomb potential is analyzed by using the approximation of a narrow resonance and close arrangement of the repulsive levels. Zh. éksp. Teor. Fiz. 115, 1337–1352 (April 1999)  相似文献   

16.
We calculate the density of states of a 2D electron gas in finite barrier height quantum wells with the explicit inclusion of the interface roughness effect. By using Feynman path-integral method, the analytic expression is derived. The results show that the 2D density of states is dependent on the RMS of the fluctuation potential. The interface roughness causes localized states below the subband edge. We also apply the theory to model the finite barrier height quantum wells in AlxGa1?xAs/GaAs.  相似文献   

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夏建白 《物理》2004,33(9):684-691
文章介绍了半导体量子阱、超晶格的基本物理,以及它在光电子领域中的应用,包括量子阱、量子线、量子点、激光器、光调制器、自电光效应器件、量子点器件等.  相似文献   

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