Central-cell And Screening Effects On The Binding Energies Of Neutral Chalcogen Impurities In Silicon

The binding energies of D0 states in S-, Se-, and Te-doped silicon crystals are calculated within a variational scheme in the effective-mass approximation and with a Chandrasekhar-type variational function for the two-electron envelopes. Central cells are modeled with a constant core potential within the impurity sphere. Screening effects for the potential and the electron-electron interaction are taken into account by means of a position-dependent dielectric function. Results are compared with recent theoretical and experimental work. It is found that central-cell effects and position-dependent screening are essential to account for the experimental data. © 1986 The American Physical Society.33128765876

Density Of States And Energy Spectra Of Hydrogenic Impurities In Quantum-well Wires

We calculate binding energies and densities of states of hydrogenic impurities in quantum-well wires with rectangular cross sections using a variational procedure within the effective-mass approximation. Calculations were performed as functions of the position of the impurity in a quantum-well wire of infinite depth and for various sizes of the wire cross section. The center of gravity of the impurity band and the density of impurity states are analyzed and compared with their quantum-well counterparts, with similarities as well as differences being discussed. Our results indicate that a proper consideration of the density of impurity states may be of relevance in the interpretation of future experimental data related to shallow impurities in quantum-well wires. © 1988 The American Physical Society.3832179218

Carrier Densities And Electron-hole Recombination Lifetimes In Gaas-(ga,al)as Quantum-well Photoluminescence

A quantum-mechanical calculation of the carrier densities and electron-hole recombination lifetimes in GaAs-(Ga,Al)As quantum wells is performed, under steady-state optical excitation conditions and in the high-temperature regime. The variables are the continuous-wave (cw) laser intensity, well widths, and acceptor distribution in the well. Radiative recombination of electrons with free holes and holes bound at neutral acceptors are considered. Our calculations for the dependence of the electron density on laser intensity are in quantitative agreement with recent experimental results for multiple asymmetric coupled quantum wells at T=300 K and for intermediate excitation. Also, results for the carrier-density-dependent e-h recombination decay time at T=155 K are in good agreement with recent experimental data in semiconductor quantum wells.75166066

Spatially Dependent Screening Calculation Of Binding Energies Of Hydrogenic Impurity States In Gaas-ga1-xalxas Quantum Wells

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The effect of spatially dependent screening is taken into account with an r-dependent dielectric response to evaluate the binding energies of shallow hydrogenic impurity states in GaAs-Ga1-xAlxAs quantum wells. A variational calculation, in the effective-mass approximation, was performed as a function of the position of the impurity in a quantum well of finite depth and for various well thicknesses. It is shown that spatially dependent screening effects can be quite important for acceptors in a GaAs-Ga1-xAlxAs quantum well due to the relatively small effective Bohr radius (22 A) of the hole. The binding energies of on-edge impurities are shown to increase, for sufficiently large well thicknesses, when the barrier potential (or the Al concentration) decreases, a behavior which contrasts with results previously reported in the literature. © 1988 The American Physical Society.3815106411064403/12595-7; FAPESP; São Paulo Research Foundation; 2007/58666-3; FAPESP; São Paulo Research Foundation; 303084/2011-1; CNPq; São Paulo Research FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Effects Of Crossed Electric And Magnetic Fields On The Electronic And Excitonic States In Bulk Gaas And Gaas Ga1-x Alx As Quantum Wells

The variational procedure in the effective-mass and parabolic-band approximations is used in order to investigate the effects of crossed electric and in-plane magnetic fields on the electronic and exciton properties in semiconductor heterostructures. Calculations are performed for bulk GaAs and GaAs Ga1-x Alx As quantum wells, for applied magnetic fields parallel to the layers and electric fields in the growth direction, and it is shown that the combined effects on the heterostructure properties of the applied crossed electric and magnetic fields and the direct coupling between the center-of-mass and internal exciton motions may be dealt with via a simple parameter representing the spatial distance between the centers of the electron and hole magnetic parabolas. Exciton properties are analyzed by using a simple hydrogenlike envelope excitonic wave function and present theoretical results are found in fair agreement with available experimental measurements on the diamagnetic shift of the photoluminescence peak position of GaAs Ga1-x Alx As quantum wells under in-plane magnetic fields. © 2007 The American Physical Society.753Whittaker, D.M., Fisher, T.A., Simmonds, P.E., Skolnick, M.S., Smith, R.S., (1991) Phys. Rev. Lett., 67, p. 887. , PRLTAO 0031-9007 10.1103/PhysRevLett.67.887Fritze, M., Perakis, I.E., Getter, A., Knox, W., Goossen, K.W., Cunningham, J.E., Jackson, S.A., (1996) Phys. Rev. Lett., 76, p. 106. , PRLTAO 0031-9007 10.1103/PhysRevLett.76.106Butov, L.V., Mintsev, A.V., Lozovik, Y.E., Campman, K.L., Gossard, A.C., (2000) Phys. Rev. B, 62, p. 1548. , PRBMDO 0163-1829 10.1103/PhysRevB.62.1548Parlangeli, A., Christianen, P.C.M., Maan, J.C., Soerensen, C.B., Lindelof, P.E., (2000) Phys. 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A 2d Honeycomb Photonic Crystal Under Applied Magnetic Fields

The band-structure properties of a photonic two-dimensional honeycomb lattice formed by cylindrical semiconductor shell rods with dielectric permitivities ε 1 and ε 2, and embedded in a background with permitivity ε 3, is studied by using an standard plane-wave expansion. The properties of bandgaps and density of states, considering dispersive dielectric responses, are investigated together with the possibility of fabricating systems with tunable photonic bandgaps, due to the Voigt magneto-optical effect, under the influence of an external magnetic field. © 2008 SPIE.7138J. D. Joannopoulos, R. D. Meade, J. N. Winn, Photonic Crystals: Molding the Flow of Light, Princeton University Press, Princeton, 1995E. Istrate and E. H. Sargent, Rev. Mod. Phys. 78, 455 (2006)Xu, C., Hu, X., Li, Y., Liu, X., Fu, R., Zi, J., (2003) Phys. Rev. B, 68, p. 193201Kee, C.-S., Kim, J.-E., Park, H.Y., Park, I., Lim, H., (2000) Phys. Rev. B, 61, p. 15523Anderson, C.M., Giapis, K.P., (1996) Phys. Rev. Lett, 77, p. 2949Rezaei, B., Kalafi, M., (2006) Optics Commun, 266, p. 159Busch, K., John, S., (1999) Phys. Rev. Lett, 83, p. 967S. B. Cavalcanti, M. de Dios-Leyva, E. Reyes-Gómez, and L. E. Oliveira, Phys. Rev. B 74, 153102 (2006)ibid., Phys. Rev. E 75, 026607 (2007)Ho, K.M., Chan, C.T., Soukoulis, C.M., (1990) Phys. Rev. Lett, 65, p. 315

Electric-field Effects On Shallow Impurity States In Gaas-(ga,al)as Quantum Wells

The influence of an applied electric field on shallow donor and acceptor states in GaAs-(Ga,Al)As quantum wells is studied. We work within the effective-mass approximation and adopt a trial envelope wave function for the impurity carrier, which leads to the exact results for vanishing applied electric fields and limiting values of the quantum-well thickness. Results for the binding energies and density of impurity states as functions of the impurity position, well thicknesses, and applied electric field are reported. Some results for the effects of electric field on the donor-related optical properties are also presented. As a general feature, the density of impurity states and impurity-related optical absorption for finite electric fields exhibit three van Hovelike singularities corresponding to the binding energies associated with impurities at the two edges of the quantum well and at the position at which the binding energy has a maximum. © 1990 The American Physical Society.42117069707

Donor-photoluminescence Line Shapes From Gaas-(ga,al)as Quantum Wells

The D°-h impurity-related photoluminescence spectra of confined donors in GaAs-(Ga,Al)As quantum wells is theoretically investigated within the effective-mass approximation. The impurity wave functions and binding energies are evaluated via a variational procedure. Calculations are performed for different well widths, temperatures, and impurity doping profiles. Typical D-h theoretical photoluminescence line shapes show peaked structures corresponding to on-center and on-edge donors in good agreement with experimental results. © 1993 The American Physical Society.4742406240

Infrared-absorption Line Shapes Of Shallow Donors In Cylindrical Quantum-well-wire Structures

A theoretical study of the intraimpurity infrared-absorption properties associated to donor-doped cylindrical GaAs-(Ga,Al)As quantum-well wires is presented. Donor binding energies and envelope wave functions are calculated within a variational scheme in the effective-mass approximation, and line strengths for intradonor transitions to excited states of 2s-, 2pz-, and 3pz-like symmetries are obtained for different photon polarizations and for donor positions varying along the radial direction of the wire. The donor-related absorption coefficients are evaluated in the case of 1s→2pz and 1s→3pz transitions for z-polarized radiation, and for different donor profiles in the quantum wire. © 1995 American Institute of Physics.7731328133

Physics of Psychophysics: Stevens and Weber-Fechner laws are transfer functions of excitable media

Sensory arrays made of coupled excitable elements can improve both their input sensitivity and dynamic range due to collective non-linear wave properties. This mechanism is studied in a neural network of electrically coupled (e.g. via gap junctions) elements subject to a Poisson signal process. The network response interpolates between a Weber-Fechner logarithmic law and a Stevens power law depending on the relative refractory period of the cell. Therefore, these non-linear transformations of the input level could be performed in the sensory periphery simply due to a basic property: the transfer function of excitable media.Comment: 4 pages, 5 figure