Electron states and related optical responses in asymmetric inverse parabolic quantum wells

ABSTRACT: The article reports the obtention of the conduction band energy states for electrons in a AlxGa1x As-based quantum well with inverse parabolic confinement. Accordingly, it has been possible to calculate the intersubband electron-transition-related optical absorption and rectification coefficients. The comparison between the results in the cases of symmetric and asymmetric rectangular barrier configurations allows to verify the possibility of the second-order optical rectification in the asymmetric case as well as a rather drastic change in the absorption coefficient as a function of the height of the inverse parabolic potential in such a configuration. Keywords: Quantum well, Nonlinear optics, Modulation doping, Electronic states

Exciton diamagnetic shift in GaAs=Ga1xAlxAs quantum wells under in-plane magnetic fields

ABSTRACT: Using a variational procedure in the effective-mass and parabolic-band approximations we investigate the effects of in-plane magnetic fields on the exciton states in single quantum wells. Exciton properties are analyzed by using a simple hydrogen-like variational envelope wave-function. Present theoretical results are compared with available experimental measurements on the diamagnetic shift of the photoluminescence peak position of quantum wells under in-plane magnetic fields [Phys. Rev. B 71 (2005) 045303]

Magnetoabsorption spectra of intraexcitonic transitions in GaAs-(Ga,Al)As semiconductor quantum wells

ABSTRACT: We present a theoretical study, within the effective-mass approximation, of the magnetoabsorption spectra of intraexcitonic terahertz transitions of light-hole and heavy-hole confined magnetoexcitons in GaAs-~Ga,Al!As quantum wells. The semiconductor quantum wells are studied under magnetic fields applied in the growth direction of the semiconductor heterostructure. The various magnetoexciton states are obtained in the effective-mass approximation by an expansion of the exciton-envelope wave functions in terms of products of hole and electron quantum-well states with appropriate Gaussian functions for the various excitonic states. Intramagnetoexciton transitions are theoretically studied by exciting the allowed excitonic transitions with s1 ~or s2! far-infrared radiation circularly polarized in the plane of the GaAs-~Ga,Al!As quantum well. Theoretical results are obtained for the intramagnetoexciton transition energies and magneto-absorption spectra associated with excitations from 1s-like to 2p6 , and 3p6-like magnetoexciton states, and found in overall agreement with optically detected resonance measurements

Binding energy and density of shallow impurity states in GaAs–(Ga, Al)As quantum wells : effects of an applied hydrostatic stress

ABSTRACT: The effects of hydrostatic stress on the binding energy and the density of shallow-donor and shallow-acceptor impurity states in a GaAs–(Ga, Al)As quantum well are calculated using a variational procedure within the effective-mass approximation. Results are for different well widths and hydrostatic stresses, as a function of the impurity position along the growth direction of the structure. We have found that in the low-pressure regime the binding energy changes linearly for both donor and acceptor impurities, independently of the sizes of the well. However, for high pressures (greater than 13.5 kbar) this is valid for acceptors but not for donors due to the -X crossover. We have shown that there are two special structures in the density of impurity states, one associated with on-centre and the other with on-edge impurities. Also, we have observed that the density of impurity states depends strongly on the applied hydrostatic stress

Binding energy of the ground and first few excited states of a shallow-donor impurity in rectangular-cross-sectional area GaAs quantum-well wires under applied electric field

ABSTRACT: Using a variational approach within the effective mass approximation we calculate the binding energy of the ground and some excited donor impurity states in quantum-well wires with rectangular and cylindrical transversal sections under the action of applied electric fields. We study the binding energy as a function of the geometry of the system, the applied electric field as well as the impurity position inside the structure. We found that the presence of the electric field breaks down the degeneracy of states for impurities symmetrically positioned within the structure, and that the geometric confinement and the electric field are determinant for the existence of bound excited states in these structures

Calculation of direct and indirect excitons in GaAs/Ga1−xAlxAs coupled double quantum wells : the effects of in-plane magnetic fields and growth-direction electric fields

ABSTRACT: The variational procedure, in the effective-mass and parabolic-band approximations, is used in order to investigate the effects of crossed electric and magnetic fields on the exciton states in GaAs/Ga1−xAlxAs coupled double quantum wells. Calculations are performed for double quantum wells under applied magnetic fields parallel to the layers and electric fields in the growth direction. The exciton envelope wave function is obtained through a variational procedure using a hydrogenic 1s-like wave function and an expansion in a complete set of trigonometric functions for the electron and hole wave functions. We take into account intersubband mixing brought about by the Coulomb interaction of electron-hole pairs in double quantum wells and present a detailed analysis of the properties of direct and indirect exciton states in these systems. The present study clearly reveals anticrossing effects on the dispersion with applied voltage or growth-direction electric field of the photoluminescence peaks associated with direct and indirect excitons. Calculated results are found in good agreement with available experimental measurements on the photoluminescence peak position associated with direct and indirect excitons in GaAs-Ga1−xAlxAs double quantum wells under growthdirection applied electric fields or under applied in-plane magnetic fields

A variational method for the description of the pressure-induced image mixing in GaAs-based quantum wells

ABSTARCT: The mixing between Γ and X conduction band valleys in GaAs–Ga1-xAlxAs quantum wells is investigated along the lines of a variational model. Trial wavefunctions are depending on a weighting variational parameter that accounts for the mixing by acting as a coefficient in the combination of both uncorrelated Γ and X states in the system. The dependencies of the calculated binding energy of a donor impurity and the correlated electron–hole photoluminescence peak energy upon hydrostatic pressure and quantum well width are presented

Photonic band structure evolution of a honeycomb lattice in the presence of an external magnetic field

ABSTRACT: A standard plane-wave expansion technique is used to investigate the evolution of the photonic band structure of a two-dimensional honeycomb lattice composed by cylindrical shell rods with dielectric permittivities 1 and 2, and embedded in a background with permittivity 3. We have considered the effect of dispersive dielectric responses as well as the influence of an externally applied magnetic field aiming to obtain efficient tunable bandgaps. Present results suggest that a combination of a doped semiconductor constituent with an anisotropic geometry, which breaks symmetry and unfolds degeneracies, provides an efficient realization of photonic systems with tunable bandgaps

Tilted electric-field and hydrostatic pressure effects on donor impurity states in cylindrical GaAs quantum disks

ABSTARCT: In this work we are devoted to the study of donor impurity states in a cylindrical GaAs quantum disk under the effects of tilted applied electric field and hydrostatic pressure. A variational procedure has been performed within the effective mass and parabolic-band approximations. For the hydrostatic pressure effects we consider the Γ-X mixing via a phenomenological procedure

Linear and nonlinear optical absorption coefficients in GaAs/Ga1−xAlxAs concentric double quantum rings : Effects of hydrostatic pressure and aluminum concentration

ABSTRACT: The linear and nonlinear intra-band optical absorption coefficients in GaAs/Ga1−xAlxAs two-dimensional concentric double quantum rings are investigated. Taking into account the combined effects of hydrostatic pressure and aluminum concentration the energies of the ground and the first excited state have been found using the effective mass approximation and the transfer matrix formalism. The energies of these states and the corresponding threshold energy of the intra-band optical transitions are examined as a function of hydrostatic pressure and aluminum concentration for different sizes of the structure. We also investigated the dependencies of the linear, nonlinear, and total optical absorption coefficients as functions of the incident photon energy for different values of hydrostatic pressure, aluminum concentration, sizes of the structure, and incident optical intensity. Its is found that the effects of the hydrostatic pressure and the aluminum concentration lead to a shifting of the resonant peaks of the intra-band optical spectrum