1,721,075 research outputs found
Valence band structure, edge states and interband absorption in quantum well wires in high magnetic fields
No full textWe present a theoretical study of the magnetic band structure of conduction and valence states in quantum-well wires in high magnetic fields. We show that hole mixing results in a very complex behavior of valence edge states with respect to conduction states, a fact which is likely to be important in magnetotransport in the quantum Hall regime. We show how the transition from one-dimensional subbands to edge states and to Landau levels can be followed by optical experiments by choosing the appropriate, linear, or circular, polarization of the light, yielding information on the one-dimensional confinement
Band-structure effects on coherent focusing in a two dimensional hole gas
No full texte investigate the coherent focusing in a weak magnetic field of a two-dimensional hole gas realized in a semiconductor heterostructure. By use of a simple model, we study how the coherence effects displayed by ballistic conduction electrons are modified if warped and nonparabolic bands are taken into account. W
Real-space approach to the multi-component envelope function problem in semiconductor heterostructures
No full textWe describe a real-space numerical method for the solution of the multicomponent-envelope-function problem in semiconductor heterostructures. The method, based on a shooting technique, provides, with a very modest computational effort, an exact solution for arbitrarily shaped one-dimensional confining potentials, including high in-plane magnetic fields. Boundary conditions at interfaces are automatically taken into account. We apply our method to the 4×4 Luttinger Hamiltonian and indicate how larger k⋅p Hamiltonians can be implemented. To demonstrate the flexibility of the method, we show the calculated hole subbands and envelope functions in a GaAs-AlxGa1-xAs quantum well with a magnetic field parallel to the interfaces and with an applied bias along the growth direction
Calculations of phonon spectra in III–V and SiGe superlattices: A tool for structural characterization
No full textThis paper reviews some of the basic concepts of phonons in semiconductor superlattices with emphasis on the aspects which are of relevance for characterization
Spin splitting in asymmetric double quantum wells: a mechanism for spin-dependent hole delocalization
No full textWe show how the breakdown of Kramers degeneracy for spin-orbit coupled bands in asymmetric double quantum wells may give rise to a new mechanism for tunneling which does not require resonant conditions. The most interesting aspect of this finding is that, in this case, there is a ‘‘spin’’-dependent delocalization of the wave function, leading to preferential tunneling of one ‘‘spin’’ state. We relate this effect to the symmetry properties of the wave functions of both single and asymmetric double quantum wells, and provide a qualitative explanation in terms of perturbation theory
ELECTRONIC-STRUCTURE OF THIN SI LAYERS IN CAF2 - HYBRIDIZATION VERSUS CONFINEMENT
No full textWe present first principle calculations of thin (1-7 double layers) silicon (111) layers in CaF2, a system with strong analogies to porous silicon. We show that the Si band gap opening is dominated by the valence band which follows the effective mass confinement picture, while the conduction band is found to flatten and shift very modestly due to hybridization effects between Si and Ca states which lead to bonding-antibonding interface states in the gap. The relevance of these results for Si-based low dimensional structures is discussed
Reconstruction and Dynamics of the W(100), Mo(100) and Cr(100) Surfaces
No full textA model has been developed that is capable of describing the structural and lattice dynamical properties of the reconstructed W(100), and the closely related Mo(100) and Cr(100), surfaces. In particular the different reconstructions (both commensurate and incommensurate) that are seen on the clean neutral surface, on a high-field FIM tip and on H-covered surfaces, are found to belong to the same T equals O surface ′′phase diagram′′
Instability, Distortion and Dynamics of the W(100) Surface
No full textA model for the reconstructions of the W(100) surface is presented. Four types of distortions are obtained, along 〈011〉, 〈001〉, 〈100〉 (commensurate), and (× 10) (incommensurate). The 〈011〉 distortion, corresponding to the observed (√2×√2)45° clean surface, is worked out in detail. A distortion magnitude of ∼ 0.35 Å is found, and a surface coherence length ξ≃15° Å close to experiment. The full vibrational spectrum, the distortion penetration, and the anisotropic surface anharmonic energies are also obtained
Effect of band mixing of the hole subbands in quantum wells on the optical transition intensities in a magnetic field
No full textThe results of interband magneto-optical measurements of GaAs quantum wells are compared with the calculated transition energies and amplitudes in a six-band envelope function approach. The evaluation of the transition matrix elements helps to explain all the essential features of the observed spectra and elucidate the complex effects of hole subbands mixing. Excitonic corrections are included in a simplified manner while a 11% larger value of the electron effective mass is needed to fit the experimental data
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