R. Riera

Hydrogenic impurities in spherical quantum dots in a magnetic field

The ground state and binding energies for a hydrogenic impurity in a spherical quantum dot within a uniform magnetic field, are calculated through the variational method in the frame of the effective-mass approximation. The trial wave functions used in the calculation are flexible enough to treat the cases of on-center, off-center, or edge impurities. Overall results show reasonable agreement when compared with other calculations. Interestingly enough, in the case of an off-center impurity, a critical point from which bulk states evolve to surface or edge states is also found. The dependence of this point on the magnetic field strength is discussed and interpreted.

One-phonon-assisted electron Raman scattering in quantum well wires and free-standing wires

The differential cross section for an electron Raman scattering process in a semiconductor quantum well wire (QWW) and in a free-standing wire of cylindrical geometry involving phonon-assisted transitions is calculated for T = 0 K. A complete description of the phonon modes of cylindrical structures embedded in another material, including a correct treatment of the mechanical and electrostatic matching conditions at the surface, is presented. We consider the Frohlich interaction to illustrate the theory for a GaAs/AlAs system. Electron states are considered to be confined within a QWW with finite and infinite potential barriers. We also assume single parabolic conduction and valence bands. The emission spectra are discussed for different scattering configurations and the selection rules for the processes are also studied. Singularities in the spectra are found and interpreted.

Electron states in a magnetic quantum ring

Electron states in a magnetic quantum ring are investigated. The electron is assumed to be confined to a plane in the presence of a magnetic field which is zero within the ring a<r<b and has a constant value B0 outside it. In this way, the perturbation caused by this field distribution is found to be quite different from that corresponding to a magnetic quantum disk, as regards electron states and circulating currents. In the case of electron states, the main effect is the splitting of the corresponding Landau levels into a sort of quasi-miniband around them and modulated by the inner radius. It is also found that probability current can change its direction depending on the missing flux quanta, a mechanism that is also governed by the size of the inner radius. Moreover, when the inner radius approaches zero, the results for a magnetic quantum disk are recovered, as expected.

Electron Raman scattering in asymmetrical multiple quantum wells

Optical properties of asymmetrical multiple quantum wells for the construction of quantum cascade lasers are calculated, and expressions for the electronic states of asymmetrical multiple quantum wells are presented. The gain and differential cross-section for an electron Raman scattering process are obtained. Also, the emission spectra for several scattering configurations are discussed, and the corresponding selection rules for the processes involved are studied; an interpretation of the singularities found in the spectra is given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.

Electron Raman scattering in semiconductor quantum wire in an external magnetic field

The differential cross-section for an electron Raman scattering process in a semiconductor quantum wire in the presence of an external magnetic field perpendicular to the plane of confinement is calculated. We assume a single parabolic conduction band. The emission spectra for different scattering configurations and the selection rules for the processes are studied. Singularities in the spectra are found and interpreted. The electron Raman scattering studied here can be used to provide direct information about the electron band and subband structure of these confinement systems. The magnetic field distribution is considered constant with value B0 inside the wire and zero outside.

Two-electron atomic systems confined within spheroidal boxes

The direct variational method is used to estimate some interesting physical properties of the He atom and the Li{sup +} ion confined within impenetrable spheroidal boxes. A comparative investigation f the ground=state energy, pressure, polarizability, dipole, and quadrupole moments with those of the He atom inside boxes with paraboloidal walls is made. The overall results show a similar qualitative behavior. However, for Li{sup +} there are quantitative differences on such properties due to its major nuclear charge, as expected. The trial wave function is constructed as a product of two hydrogenic wave functions adapted to the geometry of the confining boxes.

Multiphonon resonant Raman scattering in the semimagnetic semiconductor Cd1−xMnxTe: Fröhlich and deformation potential exciton–phonon interaction

A theory describing multiphonon resonant Raman scattering (MPRRS) processes in wide-gap diluted magnetic semiconductors is presented, with Cd1−xMnxTe as an example. The incident radiation frequency ωl is taken above the fundamental absorption region. The photoexcited electron and hole make real transitions through the LO phonon, when one considers Frohlich (F) and deformation potential (DP) interactions. The strong exchange interaction, typical of these materials, leads to a large spin splitting of the exciton states in the magnetic field. Neglecting Landau quantization, this Zeeman splitting gives rise to the formation of eight bands (two conduction and six valence ones) and ten different exciton states according to the polarization of the incident light. Explicit expressions for the MPRRS intensity of second and third order, the indirect creation and annihilation probabilities, the exciton lifetime, and the probabilities of transition between different exciton states and different types of exciton as a function of ωl and the external magnetic field are presented. The selection rules for all hot exciton transitions via exciton–photon interaction and F and DP exciton–phonon interactions are investigated. The exciton energies, as a function of B, the Mn concentration x, and the temperature T, are compared to a theoretical expression. Graphics for creation and annihilation probabilities, lifetime, and Raman intensity of second and third order are discussed.

One phonon assisted electron Raman scattering in spherical semiconductor quantum dots

Abstract The differential cross section (DCS) for an electron Raman scattering (ERS) process in a semiconductor quantum dot (QD) of spherical geometry regarding phonon-assisted transitions, is calculated for T =0 K. We present a complete description of the phonon modes of spherical structures embedded in another material, including a correct treatment of the mechanical and electrostatic matching condition at the surface. We consider the Frohlich interaction to illustrate the theory for a GaAs/AlAs system. Electron states are considered to be completely confined within the QD. We also assume single parabolic conduction and valence bands. The emission and excitation spectra are discussed for different scattering configurations and the selection rules for the processes are also studied. Singularities in the spectra are found and interpreted. The one-phonon-assisted ERS studied here can be used to provide direct information about the electron band structure of these systems.

Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire

The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire is calculated, and expressions for the electronic states are presented. The system is modeled by considering T = 0 K and also with a single parabolic conduction band, which is split into a subband system due to the confinement. The gain and differential cross-section for an electron Raman scattering process are obtained. In addition, the emission spectra for several scattering configurations are discussed, and interpretations of the singularities found in the spectra are given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.

Electron Raman scattering in semiconductor quantum well wire of cylindrical ring geometry

We study the electron states and the differential cross section for an electron Raman scattering process in a semiconductor quantum well wire of cylindrical ring geometry. The electron Raman scattering developed here can be used to provide direct information about the electron band structures of these confinement systems. We assume that the system grows in a GaAs/Al0.35Ga0.65As matrix. The system is modeled by considering T = 0 K and also a single parabolic conduction band, which is split into a sub-band system due to the confinement. The emission spectra are discussed for different scattering configurations, and the selection rules for the processes are also studied. Singularities in the spectra are found and interpreted.