Screening of Donors in GaAs/Ga1_xAlxAs as Quantum Dots.

We have carried out variation al model calculations of the binding energy of a screened donor in a spherical GaAs/Gal_x~As quantum dot as a function of the quantum dot radius. We have found that the effect of screening on the binding energy of the donor becomes more pronounced as the radius of the quantum dot decreases. This behavior is similar to that obtained earlier in model calculations of the binding energy of a donor in a quantum well, or in a quantum-well wire

Effects of hydrostatic stress on the density of impurity states and donor-related optical absorption spectra in GaAs–(Ga,Al)As quantum wells

ABSTARCT: The effects of hydrostatic stress on the density of donor impurity states and donor-related optical absorption spectra in a GaAs–(Ga,Al)As quantum well are investigated. The shallow-donor binding energy for different well widths and different values of the hydrostatic stress has been calculated. It has been found that for wider well widths the binding energy increases slowly with hydrostatic stress contrary to the behavior of the binding energy for wells with smaller widths. In particular, it has been found that the binding energy does not change appreciably with the impurity position when the width of the well is small and for large values of hydrostatic stress. Two structures in both the density of states and the optical absorption spectra, associated with impurities located close to the center and to the edges of the structure, are obtained. Also, it has been observed that the density of states and the optical absorption spectra depend strongly on the applied hydrostatic stress

Donor-related density of states and polarizability in a GaAs-(Ga, Al)As quantum-well under hydrostatic pressure and applied electric field

ABSTARCT: Theoretical calculations have been used to assess the influence of both an external electric field and hydrostatic stress on the binding energy, impurity polarizability, as a function of the impurity position and density of states for shallow-donor impurities in a GaAs–(Ga, Al)As quantum well. The binding energy maximum is shifted toward the wall at z = –L/2 of the quantum well for increasing values of electric field (keeping a constant pressure) and increasing values of pressure (keeping a constant electric field). The polarizability follows closely the behavior of the binding energy so for smaller binding energies the polarizability is large showing a more delocalized electron cloud. Also, it has been observed that the density of states depends strongly on the applied hydrostatic stress and electric field. In the absence of an electric field the energy level is degenerate for symmetrical positions of the impurities with respect to the center of the quantum well. However, this degeneracy is broken when an electric field is applied in the growth direction of the structure. Associated with this, the density of states becomes richer in structur

Shallow-donor impurity in coupled GaAs/Ga(1-x)Al(x)As quantum well wires: hydrostatic pressure and applied electric field effects

ABSTRACT: In this work we study the binding energy of the ground state for hydrogenic donor impurity in laterally coupled GaAs/Ga1 xAlxAs double quantum well wires, considering the effects of hydrostatic pressure and under the influence of a growthdirection applied electric field. We have used a variational method and the effective mass and parabolic band approximations. The low dimensional structure consists of two quantum well wires with rectangular transversal section coupled by a central Ga1 xAlxAs barrier. In the study of the effect of hydrostatic pressure, we have considered the G – X crossover in the Ga1 xAlxAs material, which is responsible for the reduction of the height of the confining potential barriers. Our results are reported for several sizes of the structure (transversal sections of the wires and barrier thickness), and we have taken into account variations of the impurity position along the growth-direction of the heterostructure, together with the influence of applied electric fields. The main findings can be summarized as: (i) for symmetric quantum-well wires (QWW) the binding energy is an even function of the growth-direction impurity position and this even symmetry breaks in the case of asymmetric structures; (ii) the coupling between the two parallel wires increases with the hydrostatic pressure due to the negative slope of the confinement potential as a function of pressure; (iii) for impurities in the central barrier the binding energy is an increasing function of the hydrostatic pressure; (iv) depending on the direction of the applied electric field and the fixed impurity position, the binding energy can behave as an increasing or decreasing step function of the applied electric field, and finally (v) for appropriate values of the wires and barrier widths the results reproduce the exact limits of 2D and 3D hydrogenic atom as well as the limits of finite and infinite potential barrier quantum wells

A quantum pseudodot system with two-dimensional pseudoharmonic potential under external magnetic and AB flux fields

Using the Nikiforov-Uvarov (NU) method, the energy levels and the wave functions of an electron confined in a two-dimensional (2D) pseudoharmonic quantum dot are calculated under the influence of temperature and an external magnetic field inside dot and Aharonov-Bohm (AB) field inside a pseudodot. magnetic field and geometrical size of quantum pseudodot. The temperature dependence energy levels for GaAs semiconductor are also calculated. The exact solutions for energy eigenvalues and wave functions are computed as functions of the chemical potential parameters, applied magnetic field strength, AB flux field, magnetic quantum number and temperature. Analytical expression for the light interband absorption coefficient and absorption threshold frequency are found as functions of appliedComment: 20 pages, 8 figures; Physica B: Condensed Matter (2012) (at press). arXiv admin note: substantial text overlap with arXiv:1111.244