Binding Energy Of Impurity Research Articles

EFFECTS OF ON-CENTER IMPURITY ON ENERGY LEVELS OF LOW-LYING STATES IN CONCENTRIC DOUBLE QUANTUM RINGS

In this paper, the electronic eigenstates and energy spectra of single and two-interacting electrons confined in a concentric double quantum rings with a perpendicular magnetic field in the presence of on-center donor and acceptor impurities are calculated using the exact diagonalization method. For a single electron case, the binding energy of on-center donor and acceptor impurities are also calculated. The effects of centrifugal, confinement and diamagnetic potentials on the binding energy are investigated. It is found that the binding energy decreases by increasing the centrifugal or confinement potential. Also, it is shown that the binding energy increases by increasing the magnetic field. The effects of on-center impurity on the energy spectrum and angular momentum transition of the lowest states are investigated for the both single and two-interacting electrons. It is found that the on-center donor impurity increases the fractional Aharonov-Bohm oscillation period while the acceptor impurity acts inversely and decreases the fractional AharonovBohm oscillation period.

Photoionization cross section of a donor impurity in a two-dimensional anisotropic quantum dot

Abstract A system of an electron with a hydrogenic impurity confined in a two-dimensional anisotropic quantum dot has been investigated. We report a calculation for the binding energy of a donor impurity. The important feature of a donor impurity in a two-dimensional anisotropic quantum dot is obtained via an analysis of the binding energy. The photoionization cross section associated with intersubband transitions has been calculated. The results are presented as a function of the incident photon energy. The results show that the photoionization cross section of a donor impurity in a two-dimensional anisotropic quantum dot is strongly affected by the degree of anisotropy and the size of the quantum dot.

Hydrogenic impurity bound polaron in a quantum dot quantum well structure

A variational approach is used within the framework of effective mass approximation to study the binding energy of the hydrogenic impurity in a spherical quantum dot quantum well (QDQW) structure. The electron- and ion-longitudinal-optical (LO) phonon interactions are taken into account in the calculation. The numerical results for the CdS/HgS QDQW structure embedded in an insulator matrix show that the binding energy is sensitive both to the size of the core and the width of the shell. The binding energy decreases with the core radius being increased, and exhibits a maximum with the shell width being increased. The LO phonon effect lowers the binding energy of the on-center impurity and decreases sharply with the shell well-width being increased.

Binding energy and diamagnetic susceptibility of an on-center hydrogenic donor impurity in a spherical quantum dot placed at the center of a cylindrical nano-wire

The binding energy and diamagnetic susceptibility of an on-center hydrogenic donor impurity in an InAs spherical quantum dot placed at the center of a GaAs cylindrical nano-wire have been investigated using finite element method in the framework of the effective mass approximation. The binding energy and diamagnetic susceptibility are calculated as a function of the dot radius, nano-wire radius and nano-wire height. The results show that as the dot radius increases (I) for a dot radius smaller than some critical value, the effect of the spherical confinement on the energy levels becomes negligible and the energies remain constant, for a dot radius larger than some specific value, the energy levels decrease (II) the ground and the first excited state binding energies increase, reach a maximum and then decrease (III) the ground state diamagnetic susceptibility increases, reach a maximum and then decreases (IV) the first excited state diamagnetic susceptibility increases, indicating two maxima and then decreases. The effects of the nano-wire dimensions on the binding energy and diamagnetic susceptibility have also been studied. We found that the binding energy and diamagnetic susceptibility decrease reach a minimum value and then increase as the nano-wire radius increases. Finally we found that as the height of the nano-wire increases the ground state binding energy decreases, reaches a minimum value and then increases but the first excited state binding energy decreases and reaches a constant value.

Combination effects of tilted electric and magnetic fields on donor binding energy in a GaAs/AlGaAs cylindrical quantum dot

We have performed a systematic study on the ground-state binding energy of an on-center donor impurity confined in a GaAs/Al0.3Ga0.7As cylindrical quantum dot (QD), subjected to simultaneously applied electric and magnetic fields. The two fields are tilted with respect to the QD growth direction and they are either parallel or perpendicular to each other. All the calculations are based on the potential morphing method which is employed within the framework of the effective-mass approximation. Our results show that when the tilted electric and magnetic fields are parallel, the magnetic shift of the donor binding energy is a monotonic function of the magnetic field strength. On the other hand, when the two fields are perpendicular to each other, the magnetic shift of the donor binding energy varies nonmonotonically with respect to the magnetic field strength, exhibiting a minimum value at a critical magnetic field strength. The position of this minimum value and its dependence on the QD size, its aspect ratio and the orientation of the tilted magnetic field is systematically investigated. Moreover, we discuss in detail the competition effects which appear in the presence of the two fields, showing that the critical line which corresponds to zero shift of the donor binding energy can be manipulated by suitably adjusting the QD size, the aspect ratio and the relative orientation of the two fields.

Hydrostatic pressure on optical absorption and refractive index changes of a shallow hydrogenic impurity in a GaAs/GaAlAs quantum wire

The effect of hydrostatic pressure on the binding energy of a hydrogenic impurity in a GaAs/GaAlAs quantum wire is discussed. Calculations have been performed using Bessel functions as an orthonormal basis within a single band effective mass approximation. Pressure induced photoionization cross section of the hydrogenic impurity is investigated. The total optical absorption and the refractive index changes as a function of normalized photon energy between the ground and the first excited state in the presence of pressure are analysed. The optical absorption coefficients and the refractive index changes strongly depend on the incident optical intensity and the pressure.

Effects of hydrostatic pressure and external electric field on the impurity binding energy in strained GaN/Al x Ga1−x N spherical quantum dots

The binding energy and Stark effect energy shifts of a shallow donor impurity state in a strained GaN/AlxGa1−xN spherical finite-potential quantum dot (QD) are calculated using a variational method based on the effective mass approximation. The binding energy is computed as a function of dot size and hydrostatic pressure. The numerical results show that the binding energy of the impurity state increases, attains a maximum value, and then decreases as the QD radius increases for any electric field. Moreover, the binding energy increases with the pressure for any size of dot. The Stark shift of the impurity energy for large dot size is much larger than that for the small dot size, and it is enhanced by the increase of electric field. We compare the binding energy of impurity state with and without strain effects, and the results show that the strain effects enhance the impurity binding energy considerably, especially for the small QD size. We also take the dielectric mismatch into account in our work.

Electric field effects on D0 binding energies in a CdTe/ZnTe spherical quantum dot

The binding energy of a neutral (D0) hydrogenic impurity located at the center of a CdTe/ZnTe spherical quantum dot (QD) in an external electric field has been investigated. Calculations for the D0 case without field are performed under the effective mass approximation on the basis of exact solutions of the Schrödinger and Poisson equations. Eigenfunctions are expressed in terms of the Whittaker and Coulomb wave functions. The results for D0 impurity energies of ground 1s and excited 2p and 3d states depend strongly on CdTe/ZnTe QD size if the QD radius is less than one effective Bohr radius. Stark shift energy levels and their wave functions in an external electric field were determined based on the variational calculations scheme within the effective mass approximation. The results show the dependence of hydrogenic impurity binding energy on the dot radius and on the external electric field strength.

External electric field and hydrostatic pressure effects on the binding energy and self-polarization of an off-center hydrogenic impurity confined in a GaAs/AlGaAs square quantum well wire

Based on the effective-mass approximation within a variational scheme, binding energy and self-polarization of hydrogenic impurity confined in a finite confining potential square quantum well wire, under the action of external electric field and hydrostatic pressure, are investigated. The binding energy and self-polarization are computed as functions of the well width, impurity position, electric field, and hydrostatic pressure. Our results show that the external electric field and hydrostatic pressure as well as the well width and impurity position have a great influence on the binding energy and self-polarization.

External electric field, hydrostatic pressure and temperature effects on the binding energy of an off-center hydrogenic impurity confined in a spherical Gaussian quantum dot

Based on the effective-mass approximation within a matrix diagonalization scheme, simultaneous effects of external electric field, hydrostatic pressure and temperature on the binding energy of an off-center hydrogenic donor confined by a spherical Gaussian potential have been calculated. The binding energy dependencies on the dot radius, the potential depth, the impurity position, the electric field strength, the hydrostatic pressure and the temperature are reported. We found that, not only the internal parameters (such as: the dot radius, the potential depth and the impurity position) but also the external perturbations (such as: electric field strength, hydrostatic pressure and temperature) have a great influence on the impurity binding energy.

The influence of polar optical phonon confinement on the binding energy of a hydrogenic impurity in quantum wires in the perpendicular electric and magnetic fields

The hydrogenic impurity binding energy in cylindrical quantum well wire with a finite confining potential including both barriers of finite height and an applied electric and magnetic fields are studied. The polaron effect on the ground-state binding energy are investigated by means of Landau-Pekar variation technique. The results for the binding energy as well as polaronic correction with taking into account polar optical phonon confinement effect are obtained as a function of the applied fields for different position of the impurity. Our calculations are compared with previous results in quantum wires of comparable dimensions.

OPTICAL INTERSUBBAND TRANSITIONS AND BINDING ENERGIES OF DONOR IMPURITIES IN Ga1-xInxNyAs1-y/GaAs/Al0.3Ga0.7As QUANTUM WELL UNDER THE ELECTRIC FIELD

The effects of nitrogen and indium mole concentration on the intersubband optical absorption for (1–2) transition and the binding energy of the shallow-donor impurities in a Ga 1-x In x N y As 1-y/ GaAs / Al 0.3 Ga 0.7 As quantum well under the electric field is theoretically calculated within the framework of the effective-mass approximation. Results are obtained for several concentrations of nitrogen and indium, and the applied electric field. The numerical results show that the intersubband transitions and the impurity binding energy strongly depend on the nitrogen and indium concentrations.

Binding energy of a donor impurity in GaAs [formula omitted] systems under electric and magnetic fields, and hydrostatic pressure

The problem of the impurity binding energy in GaAs n-type delta-doped systems is studied taking the field effect transistor as an archetypical structure. The theoretical investigation considers the effects of externally applied electric and magnetic fields as well as of hydrostatic pressure. The description of the one-dimensional potential profile is made including Hartree and exchange effects via a Thomas–Fermi-based local density approximation. The allowed energy levels are calculated within the effective mass and envelope function approximations by means of an expansion over an orthogonal set of infinite well eigenfunctions. The results for the impurity binding energy are presented also for different configurations of the impurity position within the system.

A detailed investigation of the electronic properties of a multi-layer spherical quantum dot with a parabolic confinement

In this work, we aim a detailed investigation of the electronic properties of a spherical multi-layer quantum dot with and without a hydrogenic impurity. The structure is introduced in the form of core/shell/well/shell layers. The core and well layers are defined by the parabolic electronic potentials. We carry out the effect of the core radius and layer thickness on the energy levels, their wave functions, binding energies of the impurity and the probability distributions. In order to determine the sublevel eigenvalues and eigenfunctions, the Schrödinger equation is solved full numerically by shooting method in the frame of the effective mass approximation. The results are analyzed in detail as a function of the layer thicknesses and their probable physical reasons are tried to be explained. It is found that the electronic properties and impurity binding energies are strongly depending on the layer thicknesses.

Simultaneous effects of temperature and pressure on diamagnetic susceptibility of a shallow donor in a quantum antidot

The effect of temperature and pressure, simultaneously, on the diamagnetic susceptibility and binding energy of a hydrogenic donor impurity at the center of a GaAs/Ga1−xAlxAs quantum antidot is studied within the effective mass approximation. For this goal, we first analytically solve the Schrödinger equation to obtain wavefunctions and energy levels. Then, using the electronic states, we can calculate the diamagnetic susceptibility. The results obtained from the present work reveals that (i) the diamagnetic susceptibility increases with increasing pressure, (ii) the diamagnetic susceptibility decreases by increasing temperature, (iii) the value of 〈r2〉 decreases with increasing pressure due to the quantum confinement, and (iv) an increase in the pressure enhances the binding energy for a constant temperature.

压力及屏蔽对无限深量子阱中施主结合能的影响

压力及屏蔽对无限深量子阱中施主结合能的影响

外场下压力及屏蔽对无限深量子阱中施主结合能的影响

外场下压力及屏蔽对无限深量子阱中施主结合能的影响

Effect of conduction band non-parabolicity on the donor states in zinc-blende GaN/AlGaN quantum dot

Donor binding energies of a hydrogenic impurity in a zinc-blende (ZB) GaN/AlxGa1–xN quantum dot are investigated. We have applied the variational method using 1s-hydrogenic wave-function in the framework of the single band effective mass approximation with two-parametric wave-function. The barrier height and the mass variation of AlGaN barrier are found out for different Al content in the dot. The calculations have been carried out with the inclusion of conduction band non-parabolicity using the Luttinger-Kohn model which introduces additional energy in the Hamiltonian. The numerical results show that the: 1 binding energy increases as the dot radius decreases for all Al content 2 binding energy increases with the Al content for all the dot radii 3 the inclusion of non-parabolic effects leads to more binding for all the values of dot radius and is significant for narrow wells. These results are compared with the other existing available literature.

HYDROGENIC IMPURITY BINDING ENERGY IN GaAs QUANTUM RINGS

Using a variational approach within the effective-mass approximation, we investigate the ground-state binding energy of a donor impurity in the GaAs quantum rings (QR) in the infinite confinement potential. A trial wave function with two variational parameters is used in the calculation. The binding energy as a function of the QR structure parameters and the impurity position is investigated. The results indicate that the binding energy decreases gradually as the QR structure parameters increase in the infinite confinement potential. In addition, the binding energy of the impurity exhibits a maximum as the impurity position moves along the symmetry axis of the QR from the bottom of the QR to the top. The impurity binding energy firstly increases and then decreases as the impurity moves from the internal surface of the QR to the external surface, indicating that there is a maximum.

Electric field and stepped barrier effects on hydrogenic impurity states in semiconducting stepped quantum wells

Based on the effective-mass approximation, the electric field and stepped barrier effects on hydrogenic impurity states in semiconducting stepped quantum wells (QWs) are investigated theoretically. Numerical results show that electron and impurity states are highly dependent on the electric field and stepped barrier in the stepped QWs. The applied symmetric electric fields induce asymmetric distribution of the donor binding energy in the stepped QWs. When the electric field is applied opposite to the growth direction of stepped barrier layer, it has a remarkable influence on the donor binding energy of impurities located at any position in the stepped QWs with any stepped barrier height. However, when the electric field is applied along the growth direction of the stepped barrier layer, the donor binding energy of impurities located at any impurity position is insensitive to variation of the stepped barrier height in the stepped QWs.