1,720,968 research outputs found
MAGNETOEXCITON GROUND-STATE FOR HEAVY-HOLE AND LIGHT-HOLE EXCITONS IN ANISOTROPIC SEMICONDUCTORS
No full textWe show how to compute the eigenvalues of an anisotropic Schrodinger equation for light- and heavy-hole excitons in the presence of a magnetic field using a perturbational approach and a simplified deltalike interaction potential. Performing the calculation with a potential appropriate to bulk GaAs crystal we obtain a simple relation between the binding energy at zero field and the diamagnetic shift at low fields
HEAVY-HOLE AND LIGHT-HOLE EXCITONS IN ANISOTROPIC SEMICONDUCTORS
No full textWe show how to compute the eigenvalues of an anisotropic Schroedinger equation for light- and heavy-hole excitons using a simplified deltalike interaction potential. Performing the calculation with a potential appropriate to bulk GaAs crystal, we obtain the excitonic binding energies for the heavy- and light-hole excitons, with the heavy-hole binding energy greater than that for the light hole. Inversion of this order for the case of a quantum well is discussed and explained
BOUNDARY-PROBLEMS FOR POLARITON PROPAGATION IN THIN-LAYERS AND QUANTUM-WELLS
No full textWe show how to compute the optical functions (reflection and transmission) of a semiconductor thin slab, in the vicinity of nearly degenerate exciton states. Additional boundary conditions are not required in the coherent-wave-function approach and multiple-polariton effects are included since Maxwell equations are satisfied. When the slab thickness is comparable to the exciton Bohr radius, centre of mass quantization results. When the slab thickness is smaller than the Bohr radius, we obtain quantum well polaritons. Numerical examples appropriate to GaAs are given
Excitonic polaritons in superlattices
No full textThe excitonic energies are computed in superlattices from the poles in the imaginary part of the susceptibility, using an appropriate Green's function expression for the coherent amplitude function of the electron-hole pair. Solving the Maxwell equations, the polariton states are obtained and the optical properties are computed. The procedure includes the effects of coherence between the carriers and the electromagnetic field, and it does not require any type of additional boundary conditions. Detailed calculations in GaAs/Ga1-xAlxAs superlattices show polaritonic effects in the optical properties, in particular a peculiar fine-structure lineshape of the n = 1 and n = 2 hh and Ih excitons is obtained. A comparison with similar calculations in bulk GaAs clearly shows the roles of quantum confinement and of anisotropy in the superlattice
POLARITONS IN ANISOTROPIC SEMICONDUCTORS
No full textWe show how to compute the optical properties (reflection and absorption) of anisotropic semiconductors in the exciton energy region, taking into account polariton and electron-hole coherence effects. The method is applied to a GaAs/Ga1-xAlxAs superlattice, and the modifications in the optical properties with respect to GaAs are related to the anisotropy
Polaritonic effects in superlattices
No full textWe present a method to compute the optical functions of superlattices in the excitonic energy region including the effect of the coherence between the electron-hole pair and the electromagnetic field. The electron-hole screened Coulomb potential is adopted and the valence-band structure is taken into account in the cylindrical approximation, thus separating light- and heavy-hole motions. The: calculated optical functions have poles in correspondence to the polariton eigenvalues for a multiplicity of excitonic states. We also calculate the amplitudes of higher polariton branches and the line shapes of the optical functions. Numerical examples appropriate to GaAs/Ga1-xAlxAs superlattices are given and the effect of coherence is displayed in the line shape of the excitation spectrum
MULTIPOLARITONS IN SEMICONDUCTOR THIN-LAYERS - INTERFERENCE EFFECTS IN THE REFLECTANCE SPECTRA
No full textWe consider the case of a plurality of polariton modes due to the valence band structure, and give a one-dimensional model to compute the optical functions in the exciton frequency range. Interference effects of each mode with itself and with the other modes are identified by a fine structure in the reflectivity spectrum
REFLECTIVITY OF GAAS THIN-FILMS - DENSITY-MATRIX STUDY OF POLARITON INTERFERENCE AND OF EXCITON MOTION QUANTIZATION
No full textAn accurate study of the optical properties of GaAs thin layers in the excitonic absorption region, obtained with a real-space density-matrix approach adapted to the case of thin films with degenerate valence bands is reported. The computed polarization decreases gradually to zero near the surfaces in a transition layer whose thickness decreases with increasing photon energy. The oscillatory behaviour of the reflectivity is well reproduced and can be interpreted in terms of polaritonic effects by relating the dispersion of the propagating modes to the calculated spectra. The effect of the confining material on the lineshapes and on the intensity of the peaks is also explained
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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