Binding Energy Of Hydrogenic Impurity Research Articles

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.

Barrier width and built-in electric field effects on hydrogenic impurity in wurtzite GaN/AlGaN quantum well

Based on the effective mass approximation, barrier width and built-in electric field effects on the donor binding energy of hydrogenic impurity in wurtzite (WZ) GaN/AlGaN quantum well (QW) are investigated by means of a variational method. Numerical results show that the strength of the built-in electric field inside the well layer increases and then remains constant with increasing the barrier width in WZ GaN/AlGaN QW. Moreover, for any impurity case, the donor binding energy is insensitive to the variation of the barrier width in the QW with large barrier width. In addition, it can also be found that when Al composition increases, the donor binding energy increases for impurities localized inside the right side of the QW; however, the donor binding energy decreases slightly for impurities located at the center and left side of the QW.

The hydrostatic pressure and electric field effects on the normalized binding energy of hydrogenic impurity in a GaAs/AlAs spherical quantum dot

A theoretical study of combined effects of the hydrostatic pressure and the electric field on the subband ground state energy and on the normalized ground state binding energy of a hydrogenic donor impurity on center located in a GaAs/AlAs spherical quantum dot with fixed dot radius is presented. The study is performed in the framework of the effective mass and parabolic band approximations and using a variational procedure. As a key result, it may be possible to gather high resolution maps of electric field on the studied structure with described technique.

Binding energies of shallow impurities in asymmetric strained wurtzite AlxGa1−xN/GaN/AlyGa1−yN quantum wells

The ground state binding energies of hydrogenic impurities in strained wurtzite AlxGa1−xN/GaN/AlyGa1−yN quantum wells are calculated numerically by a variational method. The dependence of the binding energy on well width, impurity location and Al concentrations of the left and right barriers is discussed, including the effect of the built-in electric field induced by spontaneous and piezoelectric polarizations. The results show that the change in binding energy with well width is more sensitive to the impurity position and barrier heights than the barrier widths, especially in asymmetric well structures where the barrier widths and/or barrier heights differ. The binding energy as a function of the impurity position in symmetric and asymmetric structures behaves like a map of the spatial distribution of the ground state wave function of the electron. It is also found that the influence on the binding energy from the Al concentration of the left barrier is more obvious than that of the right barrier.

Exact and variational calculations of a hydrogenic impurity binding energy in a multilayered spherical quantum dot

The binding energy of a central or an off-central impurity located in a multilayered spherical quantum dot has been calculated. Different effective masses and dielectric constants in the different regions of the MSQD are taken into consideration. New analytical forms for the exact solution of the radial Schrödinger equation in the absence of the impurity and in the presence of a central impurity have been introduced. The analytical forms in the presence of the central impurity have the advantage that they are valid for any electron energy negative or positive unlike the forms used hitherto. The variational method has also been applied for both central and off-central impurities. The trial wavefunction has been taken in a new form in addition to the conventional form used in previous treatments. The new form has the advantage of satisfying the boundary conditions at the interfaces in the case of different masses. It further raises the results of binding energy so that they approach the exact solution from below. The two forms have yielded new analytical expressions for the energy expectation value and binding energy.

纤锌矿GaN/AlxGa1-xN应变柱形量子点中杂质态结合能及其压力效应

In the framework of effective mass approximation,a variational method is adopted to discuss the binding energies of hydrogenic impurity in a strained wurtzite cylindrical quantum dot by considering the hydrostatic pressure.The results indicate that the binding energies of hydrogenic impurity with strain effect are higher than that without strain effect when the quantum dot height is small,but the binding energies with strain effect become lower than that without strain effect as the quantum dot height increases.It is also found that the binding energies of hydrogenic impurity decrease when the mole fraction of Al increase.In addition,the bin-ding energies of impurity increase obviously with hydrostatic pressure,and the hydrostatic pressure has a remarkable influence on the donor binding energy for small quantum dot.

Polaron effects on the binding energy of a hydrogenic impurity in parabolic quantum wires in perpendicular electric and magnetic fields

Using a variational approach, the binding energy of shallow hydrogenic impurities in a parabolic quantum wire is calculated within the effective mass approximation. The polaron effects on the ground-state binding energy in electric and magnetic fields are investigated by means of the Pekar–Landau variation technique. The results for the binding energy as well as a polaronic correction are obtained as a function of the applied fields and the impurity positions.

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.

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.

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.

Hydrostatic pressure and conduction band non-parabolicity effects on the impurity binding energy in a spherical quantum dot

The binding energy of a shallow hydrogenic impurity in a spherical quantum dot under hydrostatic pressure with square well potential is calculated using a variational approach within the effective mass approximation. The effect of conduction band non-parabolicity on these energies is also estimated. The binding energy is computed for GaAs spherical quantum dot as a function of dot size, hydrostatic pressure both in the presence and absence of the band non-parabolicity effect. Our results show that (i) the hydrostatic pressure increases the impurity binding energy when dot radius increases for a given pressure, (ii) the hydrostatic pressure with the band non-parabolicity effect effectively increases the binding energy such that the variation is large for smaller dots and (iii) the maximum contribution by the non-parabolicity effect is about 15% for narrow dots. Our results are in good agreement with Perez-Merchancano et al. [J. Phys. Condens. Matter 19 (2007) 026225] who have not considered the conduction band non-parabolicity effect.

The effect of dielectric constant mismatch on the binding energy of hydrogenic impurities in cylindrical quantum wires

The ground state binding energy dependency of hydrogenic impurities on dielectric constant mismatch is investigated in cylindrical quantum wires as a function of wire radius and alloy concentration. The calculations are done for a cylindrical GaAs/Ga 1− x Al x As system with a uniform external magnetic field applied parallel to the wire axis using the effective mass approximation and variational methods for finite confinement potentials. According to the obtained results, one can ascertain that in calculating binding energies omitting the dielectric mismatch of the system is justified for large wire radii. However, there is a sign change in contribution for the binding energy for smaller wire radii. Furthermore, the magnitude of the contribution is more pronounced for smaller wire radii and larger alloy concentrations.

Effect of temperature on the binding energy of a shallow hydrogenic impurity in a quantum well wire

In this work, we investigate the variation of the binding energy of an on-axis hydrogenic impurity in a cylindrical semiconductor GaAsalxGa1–xAs quantum well wire (QWW) with temperature, by taking into account the temperature dependance of the electron masses and dielectric constants in the quantum well and potential barrier region as well as the temperature dependence of the barrier height. This investigation is important in understanding the role such impurities can play in determining the transport properties of such systems. The results show enhancement of the binding energy as the temperature is decreased, specially for small values of wire radius.

Barrier width dependence of the donor binding energy of hydrogenic impurity in wurtzite InGaN/GaN quantum dot

Within the framework of the effective-mass approximation, the barrier width dependence of the donor binding energy of hydrogenic impurity in a cylindrical wurtzite (WZ) InGaN/GaN strained quantum dot (QD) is calculated by means of a variational procedure, considering the strong built-in electric field effect due to the spontaneous and piezoelectric polarizations. Numerical results show that the built-in electric field and the donor binding energy of the impurity located at any growth direction position are obviously dependent on the barrier width in WZ In0.1Ga0.9N/GaN strained QD with a small barrier width (<8 nm). However, the built-in electric field and the donor binding energy of the impurity located at any growth direction position are insensitive to the barrier width in WZ In0.1Ga0.9N/GaN strained QD with a large barrier width (>8 nm). Moreover, the donor binding energy of the impurity located at the right boundary of the QD is independent of the barrier width with any dot height and indium composition when the barrier width is large (>8 nm).

THE EFFECT OF POSITION DEPENDENT EFFECTIVE MASS OF HYDROGENIC IMPURITIES IN PARABOLIC GaAs/GaAlAs QUANTUM DOTS IN A STRONG MAGNETIC FIELD

The binding energy of shallow hydrogenic impurities in parabolic GaAs/GaAlAs quantum dots is calculated as a function of dot radius in the influence of magnetic field. The binding energy has been calculated following a variational procedure within the effective-mass approximation. Calculations are presented with constant effective-mass and position dependent effective masses. A finite confining potential well with depth is determined by the discontinuity of the band gap in the quantum dot and the cladding. The results show that the impurity binding energy (i) increases as the dot radius decreases for the infinite case, (ii) reaches a peak value around 1R* as the dot radius decreases and then diminishes to a limiting value corresponding to the radius for which there are no bound states in the well for the infinite case, and (iii) increases with the magnetic field. Also it is found that (i) the use of constant effective mass (0.067 m0) is justified for dot sizes ≥ a* where a* is the effective Bohr radius which is about 100 Å for GaAs , in the estimation of ionization energy and (ii) the binding energy shows complicated behavior when the position dependent mass is included for the dot size ≤ a*. These results are compared with the available existing literatures.

Diamagnetic Susceptibility of a Confined Donor in a Quantum Dot with Different Confinements

The binding energies of shallow hydrogenic impurity in a GaAs/GaAlAs quantum dot with spherical confinement, harmonic oscillator-like and rectangular well-like potentials are calculated as a function of dot radius using a variational procedure within the effective mass approximation. The calculations of the binding energy of the donor impurity as a function of the system geometry have been investigated. A comparison of the eigenstates of a hydrogenic impurity in all the confinements of dots is discussed in detail.  We have computed and compared the susceptibility for a hydrogenic donor in a spherical confinement, harmonic oscillator-like and rectangular well-like potentials for a finite QD and observe a strong influence of the shape of confining potential and geometry of the dot on the susceptibility. Keywords: Quantum dot; Quantum well wire; Quantum well; Diamagnetic susceptibility; Donor impurity. © 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v1i2.1184  Â