Search

The use of finite confining potential well model for excitons in a cylindrical quantum wire indicated that for wire radii greater than a few Bohri radii, the contribution to the exciton linewidth calculated using this model agrees with the results for the infinite well model. However for smaller wire radii, the linewidth reaches a maximum value and then decreases due an increasing probability that the exciton would be found outside the wire in the surrounding barrier.

Reserach was conducted to measure the effect of an electric field applied along the direction of carrier confinement on the exciton linewidth due to the scattering of excitons by ionized impurities in semiconducting quantum well structures. It was found that the contributions to the linewidth increased with the applied electric field except for the narrowest wells. Also, the contribution to the linewidth due to elastic scattering of the exciton is many orders of magnitude larger than that due to scattering in which the exciton is ionized.

A finite confining potential model is used to theoretically investigate the effects of an applied electric field perpendicular to well layers on the exciton linewidth due to free carrier scattering in semoconducting quantum-well structures. The free carrier-exciton linewidth broadening depends on carrier concentration, well width and temperature.

We have performed a theoretical calculation of the two photon absorption (TPA) in semiconducting quantum wires and quantum boxes in the presence of an electric field. Because of the anisotropic nature of these nanostructures, the TPA depends on the relative orientations of the electric field, the direction of polarization of the optical field, and the direction of carrier confinement in these semiconducting nanostructures. Numerical results show that the electric field decreases the TPA in quantum wires and boxes for any direction of the electric field and optical polarization. The TPA occurs below the zero field threshold energy of the semiconducting quantum wires and quantum boxes when an electric field is present. Moreover, the TPA has more structure in quantum boxes than that in quantum wires for any direction of electric field or polarization. In addition, the ratio of the TPA in the quantum wires and boxes to that in the bulk is also calculated as a function of the photon energy both in the presence and absence of the electric field. [ABSTRACT FROM AUTHOR]

We present a theoretical calculation of the effect of an electric field applied either parallel or perpendicular to the direction of confinement on the interband optical absorption of semiconducting nanostructures such as quantum wells, quantum wires, and quantum boxes. We find that the application of the electric field decreases the optical absorption coefficient for both the parallel and perpendicular to the direction of carrier confinement. The absorption is greater when the electric field is along the direction of carrier confinement than when it is perpendicular to the direction of carrier confinement. Our work differs from that of others in that we present detailed theoretical calculations of the effect of the electric field on the optical absorption coefficient and obtain analytical expressions for the absorption coefficient. We find that there are additional oscillations in the absorption above the effective band gap in addition to the structure in the absence of the electric field, which are due to the Franz–Keldysh effect for the electric field parallel to the axis of the wire and the plane of the well. Numerical results also show that there is a smaller threshold for the optical absorption of cylindrical wires than for rectangular wires with the same cross sectional area. [ABSTRACT FROM AUTHOR]

We have used a variational wave function for hydrogenic impurities in cylindrical quantum wires to calculate the dependence of the photoionization cross section of such impurities on the photon energy using the finite confining potential well model. The results are presented for various wire radii and for different locations of the impurity in the wire. We compare the results we find here to those found previously using the infinite confining potential well model. [ABSTRACT FROM AUTHOR]

We have investigated the effect of the Rashba spin splitting and a magnetic field on the energy levels of electrons in parabolic quantum dots. We find that with an increase in the Rashba parameter, the spin-orbit interaction mixes states of higher angular momentum together. In the absence of a magnetic field, the energy levels of the electrons are doubly degenerate and decrease as the Rashba parameter increases. In the presence of a magnetic field, this degeneracy is removed and the energy splitting of the spin states increases with the increase in both the Rashba parameter and the magnetic field. The Fermi energy level as a function of the magnetic field shows oscillatory behavior due to the crossings between the energy levels of the system. The magnetization of the electron gas is investigated and shows strong oscillations with the magnetic field for large values of the Rashba parameter. [ABSTRACT FROM AUTHOR]

We have calculated the effect of a transverse electric field on the ground and the first few excited states of the electrons confined in a quantum wire and used these results to examine the effect of the electric field on the intersubband optical absorption in such quantum wires. The electric field removes the degeneracies between several of the excited states in the wire, which leads to peaks in the intersubband optical absorption of the wire. The application of the electric field leads to a Stark shift of the electron energies, which is quadratic in the field at low fields but becomes almost linear in the field at high fields. The electric field shifts the peaks in a manner which depends upon the polarization of the optical field with respect to the applied electric field. We have also investigated the range of wire radii and electric fields at which the infinite well model is valid in a material where the height of the confining potential barrier is finite. We have found that for small wire radii and strong electric fields, the infinite well model breaks down. [ABSTRACT FROM AUTHOR]

We have used a variational wave function for hydrogenic impurities in cylindrical quantum wires to calculate the dependence of the photoionization cross section of such impurities on the photon energy. The calculation has been performed using the infinite confining potential well model. The results are presented as a function of photon frequency for various wire radii and for different locations of the impurity in the wire. We find that the photoionization cross section depends upon the polarization of the photons which is an effect not noted in previous work by Sali, Fliyou and Loumrhari [Physica B, 233, 196 (1997)]. For the polarization of the radiation parallel to the axis of the wire, the cross section initially increases from zero at the threshold frequency for photoionization to occur while for the polarization of the radiation perpendicular to the axis of the wire, the cross section rises steeply at the threshold frequency and then decreases with the photon frequency. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have used a variational wave function for hydrogenic impurities in spherical quantum dots to calculate the dependence of the photoionization cross section of such impurities on the energy and polarization of the photon. The calculation has been performed using both the infinite and finite confining potential well models. The results are presented for various dot radii and for different locations of the impurity in the dot. We find that for hydrogenic impurities at the center of a spherical quantum dot, the transitions take place between the impurity level associated with the ground subband and the free particle state in the second subband and the cross section is independent of the polarization of the photons. For off center impurities, the transitions take place between the impurity level associated with the ground subband and the free particle state in the ground subband when the photons are polarized along the direction connecting the impurity with the center of the dot while for photons polarized perpendicular to this direction, we find that the transitions take place between the impurity level associated with the ground subband and the free particle state in the second subband. Therefore the threshold energy for the photoionization cross section is lower for off center impurities when the photons are polarized along the direction connecting the impurity with the center of the dot than it is for on center impurities or for off center impurities for photons polarized perpendicular to this direction. [ABSTRACT FROM AUTHOR]

The two photon absorption (TPA) in semiconducting quantum wires and quantum boxes is calculated in the presence of an electric field. The TPA has more structure in quantum boxes than that in quantum wires for any direction of electric field or polarization and the ratio of the TPA in the quantum wires and boxes to that in the bulk is calculated as a function of the photon energy both in the presence and absence of the electric field.

A theoretical calculation of the effect of an electric field applied either parallel or perpendicular to the direction of confinement on the interband optical absorption of semiconducting nanostructures such as quantum wells, quantum wires, and quantum boxes are presented. The absorption of semiconducting nanostructures are found to be greater when the electric field is along the direction of carrier confinement than when it is perpendicular to the direction of carrier confinement.

The results of the effect of a transverse electric field on the ground and the first few excited states of the electrons confined in a quantum wire are used to examine the effects of the electric field o the intersubband optical absorption on such quantum wires. The findings state that for small wire radii and for strong electric fields, the infinite well model breaks down.

A variational wave function in cylindrical wires was used to calculate the dependence of photo ionization on hydrogenic impurities on the photon energy. It was found that the behaviour of the cross section varies for different polarizations.

Presents information on a study which calculated the binding energy of hydrogenic impurities in a quantum well wire as a function of the width of the quantum well wire. Impurity binding energy of quantum well wire; Results and discussion.

Presents a calculation of the free-carrier absorption for ultra thin wires fabricated from III-V compound semiconductor materials. Relation of the free-carrier absorption coefficient when phonon scattering is dominant to the transition probability for carriers; Absorption coefficient for semiconducting thin quantum-well wires; Effect of the decrease in the dimensions of the wire on the free-carrier absorption.

Presents a study that performed a variational calculation of the binding energy of the exciton confined in a two-dimensional structure. Function of molecular beam epitaxy; Reason that the study of the exciton effects has evoked interest; Effect of the confinement of electrons in a two-dimension structure on the screening of hydrogenic impurities in semiconducting inversion layers.

Presents the results of the calculation of the dielectric response function for a quasi-one-dimensional (Q1D) semiconducting system. Comparison of Q1D dielectric function to one-dimensional dielectric function; Logarithmic singularity of the dielectric function; Calculation of momentum relaxation rate for scattering from ionized impurities.