The hydrostatic pressure and temperature effects on donor impurities in GaAs/Ga1 − xAlxAs double quantum well under the external fields

The combined effects of hydrostatic pressure and temperature on donor impurity binding energy in GaAs/Ga_0.7Al_0.3As double quantum well in the presence of the electric and magnetic fields which are applied along the growth direction have been studied by using a variational technique within the effective-mass approximation. The results show that an increment in temperature results in a decrement in donor impurity binding energy while an increment in the pressure for the same temperature enhances the binding energy and the pressure effects on donor binding energy are lower than those due to the magnetic field.     

Effect of crossed electric and magnetic fields on donor impurity binding energy

By using an appropriate coordinate transformation, we have calculated variationally the ground state binding energy of a hydrogenic donor impurity in a quantum well in the presence of crossed electric and magnetic fields which are applied tilted at an angle to the layers. The dependence of the donor impurity binding energy on the well width, on the strength of the electric and magnetic fields, on the impurity position and on the directions of the external fields is discussed. PACS 71.55.Eq; 71.55.-i     

Comparison of external electric and magnetic fields effect on binding energy of hydrogenic donor impurity in different shaped quantum wells

The effects of external electric and magnetic fields on the ground state binding energy of hydrogenic donor impurity are compared in square, V-shaped, and parabolic quantum wells. With the effective-mass envelope-function approximation theory, the ground state binding energies of hydrogenic donor impurity in InGaAsP/InP QWs are calculated through the plane wave basis method. The results indicate that as the quantum well width increases, the binding energy changes most fast in SQW. When the well width is fixed, the binding energy is the largest in VQW for the donor impurity located near the center of QWs. For the smaller and larger well width, the electric field effect on binding energy is the most significant in VQW and SQW, respectively. The magnetic field effect on binding energy is the most significant in VQW. The combined effects of electric and magnetic fields on the binding energy of hydrogenic donor impurity are qualitative consistent in different shaped QWs.     

Electric field effect on the donor impurity states in zinc-blende symmetric InGaN/GaN coupled quantum dots

Based on the effective-mass approximation, the donor binding energy in a cylindrical zinc-blende (ZB) symmetric InGaN/GaN coupled quantum dots (QDs) is investigated variationally in the presence of an applied electric field. Numerical results show that the ground-state donor binding energy is highly dependent on the impurity positions, coupled QDs structure parameters and applied electric field. The applied 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 right dot, the donor binding energy has a maximum value with increasing the dot height. Moreover, the donor binding energy is the largest and insensitive to the large applied electric field (F?400 kV/cm) when the impurity is located at the center of the right dot in ZB symmetric In_0.1Ga_0.9N/GaN coupled QDs. In addition, if the impurity is located inside the right dot, the donor binding energy is insensitive to large middle barrier width (Lmb?2.5 nm) of ZB symmetric In_0.1Ga_0.9N/GaN coupled QDs.     

Hydrogenic donor states in wurtzite InGaN/GaN coupled quantum dots

The binding energies of the hydrogenic impurity in wurtzite InGaN coupled quantum dots (QDs) are 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 asymmetrical distribution of the donor binding energy with respect to the center of the coupled QDs. When the impurity is located in the center of the left dot, the donor binding energy is largest and insensitive to the barrier height of the wurtzite InGaN coupled QDs.     

Binding energy and photoionization cross section of hydrogen-like donor impurity in quantum well-wire in electric and magnetic fields

The effect of uniform electric and magnetic fields on binding energy and photoionization cross-section of an off-axis hydrogen-like donor impurity in a QWW, approximated by a cylindrical well of finite depth, is investigated within the framework of variational approach. The dependencies of the binding energy and photoionization cross-section on electric field strength, magnetic field induction, wire radius and impurity position are obtained. The cases when the polarization vector of incident radiation is parallel and perpendicular to the wire axis are both discussed.     

Binding energy of a hydrogen-like donor impurity in a quantum well-wire in magnetic and electric fields

The effect of a longitudinal magnetic and a transverse electric fields on the binding energy of a hydrogen-like donor impurity is studied for a semiconductor quantum well-wire approximated by a cylindrical well of finite depth. It is shown that the magnetic and electric fields as well as the impurity distance from the wire axis are the effective tools for the influence on the binding energy.     

Hydrostatic pressure and electric and magnetic field effects on the binding energy of a hydrogenic donor impurity in InAs Pöschl-Teller quantum ring

We consider the effects of electric and magnetic fields as well as of hydrostatic pressure on the donor binding energy in InAs Pöschl-Teller quantum rings. The ground state energy and the electron wave function are calculated within the effective mass and parabolic band approximations, using the variational method. The binding energy dependencies on the electric field strength and the hydrostatic pressure are reported for different values of quantum ring size and shape, the parameters of the Pöschl-Teller confining potential, and the magnetic field induction. The results show that the binding energy is an increasing or decreasing function of the electric field, depending on the chosen parameters of the confining potential. Also, we have observed that the binding energy is an increasing/decreasing function of hydrostatic pressure/magnetic field induction. Likewise, the impurity binding energy behaves as an increasing/decreasing function of the inner/outer radii of the quantum ring nanostructure.     

Impurity-related electronic properties in quantum dots under electric and magnetic fields

This paper presents a systematic study of the ground-state binding energies of a hydrogenic impurity in quantum dots subjected to external electric and magnetic fields.The quantum dot is modeled by superposing a lateral parabolic potential,a Gaussian potential and the energies are calculated via the finite-difference method within the effectivemass approximation.The variation of the binding energy with the lateral confinement,external field,position of the impurity,and quantum-size is studied in detail.All these factors lead to complicated binding energies of the donor,and the following results are found:(1) the binding energies of the donor increase with the increasing magnetic strength and lateral confinement,and reduce with the increasing electric strength and the dot size;(2) there is a maximum value of the binding energies as the impurity placed in different positions along the z direction;(3) the electric field destroys the symmetric behaviour of the donor binding energies as the position of the impurity.     

Hydrogenic impurity states in zinc-blende GaN/AlN coupled quantum dots

Based on the effective-mass approximation, we have calculated the donor binding energy of a hydrogenic impurity in zinc-blende (ZB) GaN/AlN coupled quantum dots (QDs) using a variational method. Numerical results show that the donor binding energy is highly dependent on the impurity position and coupled QDs structural parameters. The donor binding energy is largest when the impurity is located at the center of quantum dot. When the impurity is located at the interdot barrier edge, the donor binding energy has a minimum value with increasing the interdot barrier width.     

Electric and magnetic field effects on the binding energy of a hydrogenic impurity in quantum well wires with different shapes

In this work, we directly calculate the ground state energies for an electron in quantum well wires (QWWs) with different shapes in the presence of applied electric and magnetic fields using the finite difference method. Then, we study the ground state binding energy of a hydrogenic impurity with a variational approach. We obtain the binding energy for QWWs consisting of the combinations of square and parabolic well potential. Our results indicate that the impurity binding energy depends strongly on the structural confinement and also, on the applied electric and magnetic field.     

Rashba spin-orbit interaction effects on thermal and magnetic properties of parabolic GaAs quantum dot in the presence of donor impurity under external electric and magnetic fields

Based on the effective mass approximation, the magnetic and thermal properties of parabolic GaAs quantum dot have been investigated in the presence of Rashba Spin-Orbit interaction (RSOI), donor impurity and applied magnetic and electric fields. The exact diagonalization method has been used to solve the Hamiltonian of an electron confined in a quantum dot (QD) and obtain the eigenenergies and the binding energy of the donor impurity as a function of various QD physical parameters. We have shown the dependence of the average statistical energy, magnetization, magnetic susceptibility and heat capacity of the donor impurity in the QD on: the Rashba interaction parameter, the magnetic and electric fields, confining frequency, and temperature. The results reveal that these parameters can tune the magnetic properties of the GaAs quantum dot and flip the sign of magnetic susceptibility from negative (diamagnetic) to positive (paramagnetic) type material.     

The effect of laser field intensity on polarizability in a quantum well

A systematic study of binding energy of the ground state of a hydrogenic donor in a quantum well is calculated in the presence of a uniform electric field for different measure of laser intensities. Binding energy of the ground state of a donor is calculated, within the effective mass approximation, with the Bessel and Airy functions. Polarizability of a laser dressed donor impurity in the presence of electric field is reported. It is observed that the polarizability (i) increases as intensity of the laser field increases (ii) increases with the electric field strength and (iii) increases drastically when both the fields are applied. The dependence of the donor binding energy on the well width, the laser field intensity and the electric field is discussed. Our results are in good agreement with the previous investigations for other heterostructures in the presence of laser intensity.     

The electric field effect on binding energy of hydrogenic impurity in zinc-blende GaN/AlxGa1−xN spherical quantum dot

Within the framework of effective mass approximation, the binding energy of a hydrogenic donor impurity in zinc-blende GaN/Al_xGa_1−xN spherical quantum dot (QD) is investigated using the plane wave basis. The results show that the binding energy is highly dependent on impurity position, QD size, Al content and external field. The binding energy is largest when the donor impurity is located at the centre of the QD and the binding energy of impurity is degenerate for symmetrical positions with respect to the centre of QD without the external electric field. The maximum of the donor binding energy is shifted from the centre of QD and the degenerating energy levels for symmetrical positions with respect to the centre of QD are split in the presence of the external electric field. The binding energy is more sensitive to the external electric field for the larger QD and lower Al content. In addition, the Stark shift of the binding energy is also calculated.     

Hydrostatic pressure effects on impurity states in InAs/GaAs quantum dot

Within the framework of effective-mass approximation, the hydrostatic pressure effects on the donor binding energy of a hydrogenic impurity in InAs/GaAs self-assembled quantum dot(QD) are investigated by means of a variational method. Numerical results show that the donor binding energy increases when the hydrostatic pressure increases for any impurity position and QD size. Moreover, the hydrostatic pressure has a remarkable influence on the donor binding energy for small QD. Realistic cases, including the impurity in the QD and the surrounding barrier, are considered.     

Polaronic effects on the energy levels of a double donor impurity in quantum wells in the presence of a magnetic field

In the presence of a magnetic field the Hamiltonian of the single or double polaron bound to a helium-type donor impurity in semiconductor quantum wells (QWs) are given in the case of positively charged donor center and neutral donor center. The couplings of an electron and the impurity with various phonon modes are considered. The binding energy of the single and double bound polaron in Al_xlGa _1-xlAs/GaAs/Al_xrGa _1-xrAs QWs are calculated. The results show that for a thin well the cumulative effects of the electron-phonon coupling and the impurity-phonon coupling can contribute appreciably to the binding energy in the case of ionized donor. In the case of neutral donor the contribution of polaronic effects are not very important, however the magnetic field significantly modifies the binding energy of the double donor. The comparison between the binding energies in the case of the impurity placed at the quantum well center and at the quantum well edge is also given. Received 16 February 1999     

The multilayered spherical quantum dot under a magnetic field

The binding energy of an impurity located at the center of multilayered spherical quantum dot (MSQD) is reported as a function of the dot and barrier thickness for different alloy compositions under the influence of a magnetic field. Within the effective mass approximation, the binding energy has been calculated using the fourth order Runge-Kutta method without magnetic field. A variational approach has been employed if a magnetic field is present. The binding energy in MSQD with equal dot and barrier thickness is calculated. It is shown that the binding energy in MSQD differs from that of a single quantum dot. Also, the geometry is dominant on the binding energy for thin MSQDs, but the magnetic field becomes more effective for thick MSQDs.     

Hydrogenic impurity states in zinc-blende InGaN quantum dot

Within the framework of effective-mass approximation, the binding energy of a hydrogenic donor impurity in a zinc-blende (ZB) InGaN/GaN cylindrical quantum dot (QD) is investigated using a variational procedure. Numerical results show that the donor binding energy is highly dependent on impurity position and QD size. The donor binding energy E_b is largest when the impurity is located at the center of the QD. The donor binding energy is decreased when the dot height (radius) is increased.     

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.