Donor Impurity In Quantum Dot Research Articles

Oscillator strengths, transition probabilities and state lifetimes of on- and off-center donor impurities in quantum dots: off-center displacement, quantum size and potential-shape effects

Nonrelativistic dipole matrix elements, oscillator strengths, transition probabilities and states lifetimes of quantum dots with centered and off-centered hydrogenic impurities are studied. The effects of the off-center displacement combined to the shape of the confining potential are investigated. These optical parameters are found to be strongly modified by the parameters characterizing the confinement as well as by taking into account of the off-center shift. It is found that the oscillator strengths present a minimum for certain values of the confinement potential range and of the off-center displacement, principally due to the reaching of a low energy gap between the levels involved in the concerned transition. Likewise, the states lifetimes increase with the off-center displacement whatever the shape of the confinement potential is because of the reduction of the gap between the energies of the states when the displacement is no longer equal to zero.

Binding energy and diamagnetic susceptibility of donor impurities in quantum dots with different geometries and potentials

We study the binding energy and diamagnetic susceptibility of a donor impurity in multi-well cylindrical and spherical quantum dot systems with triangular, rectangular, saw-tooth and sinusoidal-shaped confining potentials. To tune the binding energy and diamagnetic susceptibility of a donor impurity, we used different parameters such as number of wells, composition parameter x, shape on the potential profile, shape of the quantum dot, etc. We discuss the effect of the symmetry on the step-like structure of the energy level versus the number of wells. We describe the wave function engineering (localization or delocalization) in proposed systems. We determined the situations that lead to the maximum (minimum) binding energy and diamagnetic susceptibility in the cylindrical (spherical) quantum dots. By using the number of wells, we change the monotonic increasing behavior of binding energy to a monotonic decreasing behavior. We illustrate that spherical quantum dot systems are more tunable than the cylindrical ones.

Heat capacity and entropy of Gaussian spherical quantum dot in the presence of donor impurity

The energy states of shallow donor impurity in GaAs/AlGaAs quantum dot heterostructure with Gaussian potential have been calculated by the shifted 1/N expansion method. The effects of the impurity on the ground state energy and average statistical energy have been investigated. The present calculations show that the donor impurity modifies significantly the electron energy levels of spherical quantum dot and thermal properties. In addition, we have also displayed the variations of the heat capacity and entropy of donor impurity in quantum dot with the radius, confining potential depth, dimension and temperature. The comparison shows that our results are in very good agreement with the theoretical reported work.

Energy and binding energy of donor impurity in quantum dot with Gaussian confinement

Using the method of the shifted 1/N expansion, we investigate the problem of hydrogenic-like donor impurity, located at the center of a spherical semiconductor quantum dot. We have calculated the energy eigenvalues for both ground and first excited sates under the assumption of Gaussian confining potential. The binding energies for three dimensional (3D) and two dimensional (2D) quantum dots are calculated. We show their dependence on dimensionality, dot radius and potential confinement. Our present numerical results show quantitative and qualitative very good agreement with those results obtained by diagonalization, Numerov’s integration, and Hartree–Fock methods.

Excited state absorptions of an exciton bound to an ionized donor impurity in quantum dots

An investigation of an exciton bound in a parabolic two dimensional quantum dot by a donor impurity has been carried out by using the matrix diagonalization method and the compact density-matrix approach. The linear, third-order nonlinear, total optical absorption coefficients and refractive index changes have been calculated for the s- p, p- d, and d- f transitions. The results show that the parabolic potential has a great effect on the optical absorptions. The calculated results also reveal that as the angular momentum quantum numbers of transitions increase, the optical absorption and refractive index peaks shift towards lower energies and the absorption and refractive index intensities increase.

The effect of intense laser field on the Electronic Raman Scattering of shallow donor impurities in quantum dots

The laser-field dependence of energy levels and donor-related Electronic Raman Scattering is investigated by a quasi-analytical approach. The differential cross section involved in this process is calculated as a function of secondary radiation photon energy. We find that the laser field amplitude and confinement strength have an important influence on the Raman scattering. And the transitions between lower electronic energy states are more sensitive to the laser field.

Laser field effect on the nonlinear optical properties of donor impurities in quantum dots with Gaussian potential

A detailed investigation of optical properties of donor impurities in quantum dots under the influence of laser field with Gaussian potential is performed by using the matrix diagonalization method within the effective mass approximation. Based on the computed energies and wave functions, the dependence of the nonlinear optical properties on the dot size and the potential depth is investigated. The outcome of the calculation suggests that all the factors mentioned above can influence the nonlinear optical properties strongly. We also note that the increase of the laser-dressing parameter leads to important effects on the electronic and optical properties of a quantum dot. This gives a new degree of freedom in various device applications based on the intersubband transition of electrons.

The effects of intense laser on nonlinear properties of shallow donor impurities in quantum dots with the Woods–Saxon potential

A theoretical study of the effects of intense laser fields on the nonlinear properties of donor impurities in a quantum dot with Woods–Saxon potential is performed within the matrix diagonalization method with the use of the effective mass approximation. The great advantage of our methodology is that it enables confinement regimes by varying two parameters in the model potential. The intense laser effects are included through the Floquet method, by modifying the confining potential associated to the heterostructure. Based on the computed energies and wave functions, the optical absorption coefficients and the refractive index between the ground state ( L=0) and the first excited state ( L=1) have been examined. Several configurations of the barrier height, the dot radius, the barrier slope of the confinement potential and the incident intense laser radiation have been considered. The outcome of the calculation suggests that all the factors mentioned above can influence the nonlinear optical properties strongly.

Nonlinear optical properties of an exciton bound to an ionized donor impurity in quantum dots

In this study, a detailed investigation of the nonlinear optical properties of the ( D + , X ) complex in a disc-like parabolic quantum dot has been carried out by using the matrix diagonalization method and the compact density-matrix approach. First, the numeric calculations and analysis of the oscillator strength of intersubband quantum transition from the ground state into the first excited state at the varying confinement frequency have been performed. Second, the linear, third-order nonlinear, and total absorption coefficients and refractive indices have been investigated. It is observed that the confinement frequency of QDs and the intensity of the illumination have drastic effects on the nonlinear optical properties. In addition, we find that all kinds of absorption coefficients and refractive indices of an exciton in QDs shift to lower energies and their peak values have considerably decreases induced by the impurity.

Theoretical study of positive and negative donor impurity in quantum dot, quantum well limit and quantum wire limit

We compare the binding energy of positive (D +) and negative (D −) charged donor impurities on- and off-center confined in a fully three dimension (3-D) anisotropic cylindrical quantum dot (CQD) with a finite barrier height. Two-parameter anisotropic trial wave function is used, to explore the quantum wire wells (QWW), and the quantum well (QW) limits. A quantitative study for the behavior of the binding energy of D + and D − is introduced. It has been shown that the donor's binding energies dependent strongly on CQD radius R, and it has been found unexpected behavior of D +. The complex, when D 0 bound heavy or light hole to form ( D hh + ) or ( D 1 h + ) , the binding energy is examined. It has been concluded that D 1 h + is more bounded (higher binding energy) than D hh + . Moreover for a certain CQD we have calculated the binding energy of the off-center impurities. It has been found that D + binding energy increases when impurity ion is moved away from the center of the examined nanostructures, but the D − binding energy decreases when impurity ion moves away from the center.

Excited states and spontaneous transition lifetimes of donor impurities in quantum dots

AbstractWe calculate the 2p→1s‐like transition energy and the spontaneous lifetime of an on‐center shallow donor impurity in a spherical parabolic GaAs‐(Ga,Al)As quantum dot (PQD) as a function of the radius of the structure and the strength of an applied electric field. In our calculations we use a variational method, within the effective mass and dipolar approximations. We find that the spontaneous lifetimes increase with the radius of the PQD and the applied electric field. In this direction our results revel that the electric field can be used to suppress the electron‐phonon interaction driving to the increasing of the 2p‐1s spontaneous life‐time, showing the feasibility of using impurity states to be used in quantum computing developments. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Far‐infrared optical spectrum of donor impurities in quantum dots in a magnetic field

AbstractWe report calculations for far‐infrared absorption in GaAs/Ga1–xAlxAs quantum dots doped with shallow‐donor impurities in the presence of a magnetic field. The wave functions and the eigenvalues are obtained in the effective‐mass approximation by using a variational approach in which the ground and excited magneto‐impurity states are simultaneously obtained. The allowed intra‐donor transitions have been investigated by using far‐infrared radiation circularly polarized in the plane perpendicular to the magnetic field. We present results for the absorption coefficient as a function of the photon energy for several field strengths and arbitrary impurity positions. We have found that, as a consequence of the quantum dot confinement the infrared magneto‐absorption strongly depends on the position of the impurity in the dot.