C.A. Duque

Effects of applied magnetic fields and hydrostatic pressure on the optical transitions in self-assembled InAs/GaAs quantum dots

A theoretical study of the photoluminescence peak energies in InAs self-assembled quantum dots embedded in a GaAs matrix in the presence of magnetic fields applied perpendicular to the sample plane is performed. The effective mass approximation and a parabolic potential cylinder-shaped model for the InAs quantum dots are used to describe the effects of magnetic field and hydrostatic pressure on the correlated electron-hole transition energies. Theoretical results are found in quite good agreement with available experimental measurements for InAs/GaAs self-assembled quantum dots.

Simultaneous effects of hydrostatic stress and an electric field on donors in a GaAs-(Ga, Al)As quantum well

Theoretical calculations on the influence of both an external electric field and hydrostatic stress on the binding energy and impurity polarizability of shallow-donor impurities in an isolated GaAs-(Ga, Al)As quantum well are presented. A variational procedure within the effective-mass approximation is considered. The pressure-related Γ-X crossover is taken into account. As a general feature, we observe that the binding energy increases as the length of the well decreases. For the low-pressure regime we observe a linearly binding energy behaviour. For the high-pressure regime the simultaneous effects of the barrier height and the applied electric field bend the binding energy curves towards smaller values. For low hydrostatic pressures the impurity polarization remains constant in all cases with an increasing value as the field increases. This constant behaviour shows that the small variations in well width, effective mass, and dielectric constant with pressure do not appreciably affect polarizability. For high hydrostatic pressure, we see a non-linear increase in polarizability, mainly due to the decrease of barrier height as a result of the external pressure, which allows further deformation of the impurity.

Uniaxial stress dependence of the binding energy of shallow donor impurities in GaAs–(Ga,Al)As quantum dots

We have studied the effects of an uniaxial stress on the binding energy of a shallow donor impurity in a parallelepiped-shaped GaAs–(Ga,Al)As quantum dot. In the calculations we have used a variational technique within the effective-mass approximation. The stress was applied in the z direction and the donor impurity was located at various positions along the z axis. Our results show that the donor binding energy increases with increasing stress and for decreasing sizes of the quantum dot. Also, we have found that the binding energy for various values of the donor position along the z axis for constant quantum well box size increases with the proximity of the impurity to the center of the structure. Moreover, we obtain the shallow-donor binding energies as functions of uniaxial stress in the limit in which the quantum dot turns into either a quantum well or a quantum-well wire.

Binding energy and polarizability in GaAs–(Ga,Al)As quantum-well wires

Abstract By means of a variational scheme and in the effective-mass approximation we have calculated the binding energy of shallow-donor impurities in rectangular-transversal section GaAs–(Ga,Al)As quantum-well wires under an applied electric field. We have considered an infinite confinement model to describe the barriers on the wire boundaries. Depending on the transversal sizes, we can reproduce the results for the infinite quantum wells. We present the results for donor binding energies and polarizabilities of the wires. Our results are in good agreement with previous theoretical findings. This work gives very important information about the binding energy and polarizability that can be taken into account in experimental work related to absorption processes, and carrier dynamics, associated with impurities in these heterostructures.

Electron-hole transitions in self-assembled InAs/GaAs quantum dots: Effects of applied magnetic fields and hydrostatic pressure

A theoretical study of the effects of applied magnetic fields and hydrostatic pressure on the electron-hole transition energies in self-assembled InAs/GaAs quantum dots is presented. The effective-mass approximation and a model of a cylindrical-shaped quantum dot with in-plane parabolic potential have been used to describe the InAs/GaAs quantum dots. Present theoretical results are in quite good agreement with experimental measurements of the magnetic field and pressure dependence of the exciton transition energies in InAs/GaAs self-assembled quantum dots.

Electric field effects on the states of a donor impurity in rectangular cross-section vacuum/GaAs/vacuum quantum-well wires

We present a study of the role of the electric field on the binding energy of the ground and first few excited states of a shallow impurity in a rectangular cross-sectional area vacuum/GaAs/vacuum quantum-well wire (QWW), where the electric field is applied perpendicular to the symmetry axis of the wire. Using the effective-mass approximation within a variational scheme we calculate the binding energy of the 1s-like ground state as well as that of some excited states (2s-, 2px-, and 2pz-like) as a function of the geometry, applied electric field, and donor-impurity position. 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. Future interpretations of optical phenomena related with shallow donor impurities in vacuum/GaAs/vacuum QWWs, in which the effects of an applied electric...

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

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 Γ-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 and photoionization cross-section in GaAs quantum well-wires and quantum dots: magnetic field and hydrostatic pressure effects

Using a variational procedure for a hydrogenic donor-impurity we have investigated the influence of an axial magnetic field and hydrostatic pressure in the binding energy and the impurity-related photoionization cross-section in 1D and 0D GaAs low dimensional systems. Our results are given as a function of the radius, the impurity position, the polarization of the photon, the applied magnetic field, the normalized photon energy, and the hydrostatic pressure. In order to describe the G-X mixing in the Ga1-xAlxAs layer, we use a phenomenological procedure to describe the variation of the potential barrier that confines the carriers in the GaAs layer. Our results agree with previous theoretical investigations in the limit of atmospheric pressure. We found that the binding energy and the photoionization cross-section depend on the size of the structures, the potential well height, the hydrostatic pressure, and the magnetic field.

Donor-related optical absorption spectra for a GaAs-Ga0.7Al0.3As double quantum well under hydrostatic pressure and applied electric field effects

The hydrostatic-pressure and applied electric field dependencies of the binding energy and the optical-absorption spectra, associated with transitions between the n = 1 valence subband and the donor-impurity band, in symmetrical and asymmetrical GaAs-Ga1-xAlxAs double quantum-well structures are calculated using a variational procedure within the effective-mass approximation. Results are obtained for different well and barrier widths, shallow-donor impurity positions, hydrostatic pressure, and applied electric field.

Donor impurity-related linear and nonlinear intraband optical absorption coefficients in quantum ring: effects of applied electric field and hydrostatic pressure

AbstractThe linear and nonlinear intraband optical absorption coefficients in GaAs three-dimensional single quantum rings are investigated. Taking into account the combined effects of hydrostatic pressure and electric field, applied along the growth direction of the heterostructure, the energies of the ground and first excited states of a donor impurity have been found using the effective mass approximation and a variational method. The energies of these states are examined as functions of the dimensions of the structure, electric field, and hydrostatic pressure. We have also investigated the dependencies of the linear, nonlinear, and total optical absorption coefficients as a function of incident photon energy for several configurations of the system. It is found that the variation of distinct sizes of the structure leads to either a redshift and/or a blueshift of the resonant peaks of the intraband optical spectrum. In addition, we have found that the application of an electric field leads to a redshift, whereas the influence of hydrostatic pressure leads to a blueshift (in the case of on-ring-center donor impurity position) of the resonant peaks of the intraband optical spectrum.