Binding Energy Of Impurity Research Articles

Binding energy of an off-center donor impurity in ellipsoidal quantum dot with parabolic confinement potential

The binding energy of an off-center hydrogenic donor impurity in weakly oblate Ellipsoidal Quantum Dot (EQD), using the expansion method within the framework of effective mass approximation in strong confinement, is investigated. In this regard, the binding energies of different states of GaAs structures, as functions of the donor position and ellipticity parameter, are calculated. The results show that variations of binding energies are proportional to the ellipticity constant, the dot dimension and the location of impurity.

Effect of magnetic field on the impurity binding energy of the excited states in spherical quantum dot

The effect of external magnetic field on the excited state energies in a spherical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic field, the energy would be increased. The results obtained by this method were compared with the previous investigations.

BINDING ENERGIES OF HYDROGENIC IMPURITIES ON-CENTER AND OFF-CENTER IN CYLINDRICAL QUANTUM DOTS UNDER ELECTRIC AND MAGNETIC FIELDS

The ground-state binding energies of a hydrogenic impurity in cylindrical quantum dots (QDs) subjected to external electric and magnetic fields are investigated using the finite-difference method within the quasi-one-dimensional effective potential model. The QD is modeled by superposing a square-well potential and a strong lateral confinement potential by the combination of a parabolic potential and a changeable magnetic field. We define an effective radius of a cylindrical QD which can describe the strength of the lateral confinement. The effects of the electric fields are less important when the effective radius is very tiny, and the effects are manifested as the effective radius increases. Meanwhile, one finds that the binding energies highly depend on the impurity positions under the applied transverse fields. When the impurity is located at the right half of the cylinder, the electric field pushes the electron to the left side, then the binding energy decreases; when the impurity is located at the left, the binding energy first increases and reaches a peak value, then deceases with the electric field.

EXTERNAL ELECTRIC FIELD EFFECT ON THE HYDROGENIC DONOR IMPURITY IN ZINC-BLENDE GaN/AlGaN CYLINDRICAL QUANTUM WELL WIRE

The binding energy of a hydrogenic donor impurity in a zinc-blende GaN / AlGaN cylindrical quantum well wire (QWW) is calculated in the framework of effective-mass envelope-function theory using the plane wave basis. It is shown that the donor binding energy is highly dependent on the impurity position, the radius of the wire and the external electric field. In addition, Stark shift dependence on the radius of the QWW and the external electric field is also calculated. The donor binding energy has a maximum when the impurity is located at the center of the QWW. The donor binding energy decreases with the increase of the external electric field, but stark shift increases with the increase of the external electric field or the radius of the QWW.

Positive and Negative Donor Impurity in an InAs/AlAs Quantum Wire

Binding energies of positive and negative charged donor impurities in an InAs/AlAs cylindrical quantum wire are investigated. Numerical calculations are performed using the variational procedure within the single band effective mass approximation. We assume that the impurity is located at the axis of the wire. The interband optical transition with and without the exciton is computed as a function of wire radius. The valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. Neutral shallow donors comprise a positively charged donor and a single bound electron. It is observed that (i) negative trions have a higher binding energy than positive trions, (ii) the binding energy of the heavy-hole exciton is much larger than that of the light-hole exciton due to different hole mass values (iii) the exciton binding energy and the interband emission energy are both increased when the radius of the cylindrical quantum wire is decreased and (iv) the effect of exciton influences the interband emission energy. Our results are in good agreement with the recent published results. Keywords: Quantum wire; Impurity level; Binding energy; Excitons. © 2010 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v2i3.4715 J. Sci. Res. 2 (3), 433-441 (2010)

Binding energy of shallow donor impurity in asymmetric quantum wells

The binding energy of the shallow donor impurity in the asymmetric semiconductor quantum well is theoretically investigated. It is shown that, when using the variational method, a pronounced binding energy dependence of the quantum well parameters can be obtained. Moreover, the binding energy depends significantly on the impurity position and the well shape.

Hydrogenic impurity states in zinc-blende symmetric InGaN/GaN multiple quantum dots

Based on the effective-mass approximation, the ground-state donor binding energy of hydrogenic impurity in a cylindrical zinc-blende (ZB) symmetric InGaN/GaN multiple quantum dots (QDs) is investigated variationally. It is found that the donor binding energy has a maximum value when the impurity is located at the center of the QDs. Numerical results also show that, for the impurity located at the center of the middle QD, the donor binding energy has a minimum value with increase in the middle barrier width. The donor binding energy is insensitive to the increment of the middle barrier width when the middle barrier width is large. Moreover, we find that the donor binding energy is basically invariable with increase in the Indium (In) composition when the impurity is located at the center of the middle barrier.

Simultaneous effects of hydrostatic pressure and temperature on the binding energy of hydrogenic impurity in cylindrical quantum well wires

The effect of hydrostatic pressure and temperature on the ground state binding energy of hydrogenic impurities is investigated in a GaAs/Ga 0.7Al 0.3As cylindrical quantum well wire as a function of the wire radius. The calculations are performed using a variational procedure within the effective mass approximation for a finite confinement potential for various values of the hydrostatic pressure and temperatures. The results are compared with the available data in literature and found to be in a good agreement with them.

A new confinement potential in spherical quantum dots: Modified Gaussian potential

A new confinement potential for spherical quantum dots, called the modified Gaussian potential (MGP), is studied. In the present work, the following problems are investigated within the effective-mass approximation: (i) the one-electron energy spectra, (ii) wave functions, (iii) the problem of existence of a bound electron state, and (iv) the binding energy of center and off-center hydrogenic donor impurities. For zero angular momentum ( l = 0 ) , the new confinement potential is sufficiently flexible to obtain analytically the spectral energy and wave functions. The results obtained from the present work show that (i) the new potential is suitable for predicting the spectral energy and wave functions, and (ii) the geometrical sizes of the quantum dot play the important roles on the energy levels, wave functions, the binding energy, and the existence of a bound electron state.

Hydrogenic impurity states in wurtzite symmetric ZnO/MgZnO coupled quantum dots

Within the framework of effective-mass approximation, the ground-state donor binding energy of a hydrogenic impurity in cylindrical wurtzite (WZ) symmetric ZnO/MgZnO strained coupled quantum dots (QDs) is calculated by means of a variational method, considering the strong built-in electric field induced by the spontaneous and piezoelectric polarizations. Numerical results show that the strong built-in electric field induces an asymmetric distribution of the donor binding energy with respect to the center of the coupled QDs. When the impurity is located at the center of the dot which is opposite to the growth direction, the donor binding energy has a maximum value with increasing dot height; and it is also insensitive to the middle barrier width if the middle barrier width is large. Moreover, numerical results also indicate that the donor binding energy of impurity located at the right boundary of the dot which is opposite to the growth direction is insensitive to the Mg composition if the Mg composition is large.

External electric field effect on the hydrogenic donor impurity in zinc-blende InGaN/GaN cylindrical quantum well wire

The binding energy of a hydrogenic donor impurity in a zinc-blende InGaN/GaN cylindrical quantum well wire (QWW) is calculated in the framework of effective-mass envelope-function theory using the plane wave basis. It is shown that the donor binding energy is highly dependent on impurity position, radius of the wire, and external electric field. In addition, Stark shift dependence on radius of the QWW and external electric field is also calculated. The donor binding energy has a maximum when the impurity is located on the axis of the QWW. The donor binding energy decreases with increase in the external electric field, while Stark shift increases with increase in the external electric field or radius of the QWW.

Combined effects of hydrostatic pressure and electric field on the donor binding energy and polarizability in laterally coupled double InAs/GaAs quantum-well wires

This work is concerned with the theoretical study of the combined effects of applied electric field and hydrostatic pressure on the binding energy and impurity polarizability of a donor impurity in laterally coupled double InAs/GaAs quantum-well wires. calculations have been made in the effective mass and parabolic band approximations and using a variational method. The results are reported for different configurations of wire and barriers widths, impurity position, and electric field and hydrostatic pressure strengths. Our results show that for symmetrical structures the binding energy is an even function of the impurity position along the growth direction of the structure. Also, we found that for hydrostatic pressure strength up to 38 kbar, the binding energy increases linearly with hydrostatic pressure, while for larger values of hydrostatic pressure the binding energy has a nonlinear behavior. Finally, we found that the hydrostatic pressure can increase the coupling between the two parallel quantum well wires.

Donor in cylindrical quantum well wire under the action of an applied magnetic field

In this paper we present a calculation of the binding energy of a donor impurity in a cylindrical GaAs-Ga 0.6Al 0.4As quantum well wire (QWW) as a function of an applied magnetic field for different wire radii and different positions of the donor. The model considers an infinite length QWW with a carrier that is confined laterally by a parabolic potential and the presence of a uniform magnetic field applied parallel to the wire axis. The 1s-like impurity state is considered using the effective-mass approximation within the variational approach. We found that for a given wire radius the binding energy of the impurity increases with the magnetic field and that for a given magnetic field value it decreases with wire radius. Our results are in good agreement with previous theoretical reports.

Donor impurity in InGaN/GaN asymmetric multiple quantum wells

Based on the effective-mass approximation, the binding energy of a donor impurity in zinc-blende (ZB) InGaN/GaN asymmetric multiple quantum wells (AMQWs) is investigated variationally. Numerical results show that the ground-state donor binding energy is highly dependent on the impurity positions and the AMQWs structure parameters. The donor binding energy has a maximum value and the impurity position of the maximum value is localized inside the wide well of the AMQWs. Moreover, the variation of any well width of the AMQWs has a remarkable influence on the donor binding energy. In particular, for the impurity localized inside the wide well, the donor binding energy is insensitive to the increment of the inter-well barrier width when the inter-well barrier width is large.

Effects of an intense, high-frequency laser field on the intersubband transitions and impurity binding energy in semiconductor quantum wells

Within the framework of effective-mass approximation, using a variational method, the effect of high-frequency laser field on intersubband transitions and the binding energy of shallow-donor impurities in a semiconductor quantum well are investigated. We have found that the increase of the laser-dressing parameter leads to important effects on the electronic and optical properties of a quantum well. This gives a new degree of freedom in various device applications based on the intersubband transition of electrons.

The effects of temperature and hydrostatic pressure on the photoionization cross-section and binding energy of impurities in quantum-well wires

Using a variational approach, we have calculated the donor impurity related photoionization cross-section and impurity binding in GaAs/GaAlAs quantum-well wires under different temperature and hydrostatic pressure conditions. Our calculation have revealed the dependence of the photoionization cross-section and the impurity binding on temperature and hydrostatic pressure.

Polaronic excitons in a [formula omitted] double-quantum-well semiconductor heterostructure

Binding energies of a hydrogenic donor impurity in a GaAs/Ga 1− x Al x As double quantum well are investigated. We have applied the variational method using a ground state hydrogenic wavefunction, in the framework of the single-band effective mass approximation. The binding energy is calculated for different Al contents and different barrier sizes. A position dependent binding energy is reported for different well widths. The donor exciton binding energy with the inclusion of valence band anisotropy is investigated as a function of the well width. The 2D Hartree–Fock spatial dielectric function and polaronic effects have been employed in our calculations. The results show that the binding energy is higher when the impurity is at the well centre and lower when the impurity is at the barrier centre. The exciton binding energy is enhanced upon the inclusion of the spatial dielectric function and the polaronic effect. The exciton has an influence on the interband emission energy. The results are compared with ones from the available literature.

General properties of confined hydrogenic impurities in spherical quantum dots

The effective-mass approximation using a plane wave basis method is applied to calculate the general properties of the ground state of the binding energy of hydrogenic impurities in spherical quantum dots. In particular, the effects of quantum-size, donor-position and electric field are investigated in detail. The present calculations were carried out for different potential shapes which correspond to four models of possible spherical quantum dots configurations. It is found that this binding energy is strongly linked to the electronic confinement and that its properties can be predicted in general from the knowledge of the electronic probability density and of the position of the impurity.

Effects of Implantation Temperature on Sheet and Contact Resistance of Heavily Al Implanted 4H-SiC

Effects of implantation temperature on electrical properties of heavily-Al-doped 4H-SiC layer formed with Al implantation have been investigated. To form the p++ 4H-SiC with the original 4H-stacking structure, the implantation temperature above 175 °C is needed. A decrease in the implantation temperature below 250 °C leads to an increase in the NA-ND. It is suggested that an increase in the density of vacancies with a decrease in the implantation temperature promotes the Al substitution to lattice sites during activation annealing. The lower-temperature implantation also causes a decrease in activation energy for the p-type electrical conduction and a decrease in p-type ohmic contact resistivity. We presume that the increase in the Al acceptors at low-implantation temperatures gives expansion of the impurity bands and formation of valence band tail-states, causing the decrease in the impurity binding energy. The properties obtained with the lower-temperature implantation are desirable for practical applications especially at low temperatures.

Laser-induced reshaping of the density of impurity states in GaAs/AlGaAs nanowires

The binding energy of shallow-donor impurities in a cylindrical quantum well wire irradiated by an intense non-resonant laser field is calculated within the effective mass approximation by using a variational procedure. Accurate laser-dressing effects are considered for both the confinement potential of the wire and the Coulomb potential of the impurity. The computation of the ground state subband energy eigenfunctions for different laser field intensities is based on a bidimensional finite element method. Important changes of the electron probability density under intense laser field conditions are predicted. The study reveals that the laser field compete with the quantum confinement and breaks down the degeneracy of states for donors symmetrically positioned within the nanostructure. A proper analysis of the density of impurity states is found to be essential for controlling the optical emission related to shallow donors in semiconductor quantum wires.