On-center Hydrogenic Impurity Research Articles

Electronic states and optical characteristics of GaAs Spherical quantum dot based on Konwent-like confining potential: Role of the hydrogenic impurity and structure parameters

In this study, we investigate for the first time the electronic states and optical characteristics of GaAs quantum dot with an on-center hydrogenic impurity using a Konwent-like spherical potential well. We numerically solve the radial component of Schrodinger equation in the framework of the effective-mass approximation (EMA) to determine the energy level structure and wavefunctions of the system. We then calculate the optical absorption coefficient (OAC) of the system using Fermi's golden rule and discuss the influence of the energy separation (E1p-E1 s), the dipole matrix element and the parameters of the potential on the OAC. We calculate and compare radial distributions for the lowest four electronic states (i.e., 1 s, 1p, 2 s, and 2p) of the system with and without the on-center impurity for different values of the parameters of the Konwent-like potential. Our results show how vary the parameters of the potential to tune the OAC towards red or blue shift and also to control its amplitude.

Effect of magnetic field on absorption coefficients, refractive index changes and group index of spherical quantum dot with hydrogenic impurity

Optical properties of a spherical quantum dot (QD) with an on-center hydrogenic impurity in the external static magnetic field are studied. Energies and wavefunctions of the impurity electron are calculated using the Lagrange mesh method. Expressions for the optical absorption coefficients (ACs), refractive index changes (RICs) and group index (GI) are derived with the help of the density matrix formalism for a two-level system, and analyzed from the theoretical point of view. The behavior of ACs, RICs and GI with respect to the incident photon energy is examined, as well as their dependence on the magnetic field strength, laser intensity and relaxation time. It is observed that all of these parameters strongly affect the studied properties of the QD.

The effects of polaronic mass and conduction band non-parabolicity on a donor binding energy under the simultaneous effect of pressure and temperature basing on the numerical FEM in a spherical quantum dot

Basing on the numerical Finite Element Method (FEM), we have investigated the influences of polaronic mass and conduction band non-parabolicity on the binding energy of the ground state of an on-center hydrogenic donor impurity in a spherical GaAs/Ga1−xAlxAs quantum dot structure. The calculations have been made with a realistic potential barrier height in the framework of the effective mass approximation including the combined effect of hydrostatic pressure and temperature. The donor binding energy is computed as a function of dot size, Al concentration x, hydrostatic pressure and temperature both in the absence and presence of polaronic mass and conduction band non-parabolicity effects. We have taken into account the electronic effective mass, dielectric constant, and conduction band offset between the dot and barriers varying with pressure and temperature. It has been found that the binding energy is strongly affected by the effect of polaronic mass and conduction band non-parabolicity for narrow quantum dot and large Al concentration x. The results show again that the donor binding energy increases linearly with the pressure in direct gap regime and its variation is larger for narrower dots only and drops slightly with the temperature. A good agreement is obtained with the existing literature values.

Group velocity of light in a three level ladder-type spherical quantum dot with hydrogenic impurity

In this paper we analyzed the group velocity of light and slow light in the spherical quantum dot with on-center hydrogenic impurity. To do this, we considered a ladder like system which consist of three energy levels of hydrogen impurity 1s0, 2p−1, and 3d−2, together with the probe and control laser fields, which induce σ− transitions. The Scrödinger equation is solved in order to obtain eigenfunctions, eigenvalues and dipole transition moments. Optical Bloch equations are than solved in a stationary regime, and the group velocity of probe laser field examined in detail. Dependence of the group velocity of light is discussed as a function of the spherical quantum dot radius, probe field frequency, control laser field intensity and control laser field detuning.

Hydrogenic impurity, external electric and magnetic fields effects on the nonlinear optical properties of a multi-layer spherical quantum dot

In this work, effects of an on-center hydrogenic impurity, external electric and magnetic fields on the optical rectification coefficient (ORC), second and third harmonic generations (SHG and THG) of a multi-layer spherical quantum dot (MLSQD) are studied. Energy eigenvalues and eigenvectors are calculated using the direct matrix diagonalization method and optical properties are obtained using the compact density matrix approach. Our results reveal that the hydrogenic impurity and external fields have a great influence on these optical quantities. Hydrogenic impurity reduces the magnitude of the resonant peaks and shifts them to the higher energies. An increase in the magnetic (electric) field, leads to increase (decrease) the interval energies and the dipole moment matrix elements. Therefore, resonant peaks of these optical quantities find an obvious blue (red) shift and their magnitudes enhance (diminish) with increasing the external magnetic (electric) field.

Effect of hydrostatic pressure on diamagnetic susceptibility of hydrogenic donor impurity in core/shell/shell spherical quantum dot with Kratzer confining potential

Abstact The effect of the hydrostatic pressure on diamagnetic susceptibility of on-center hydrogenic donor impurity in G a 1 − x 1 A l x 1 A s / G a A s / G a 1 − x 2 A l x 2 A s core/shell/shell structure with Kratzer confining potential has been theoretically investigated in the framework of the effective mass approximation. The diamagnetic susceptibility has been calculated as a function of the characteristic parameters of Kratzer confining potential. With the increase of the hydrostatic pressure, the diamagnetic susceptibility increases. The same dependence from the depth of the Kratzer potential was obtained. However, the value of the diamagnetic susceptibility became saturated. The results show that with the potential minimum point increase, the diamagnetic susceptibility increases until some critical value, after which it decreases.

Electromagnetically induced transparency in a spherical quantum dot with hydrogenic impurity in a four level ladder configuration

The present paper analyses the electromagnetically induced transparency (EIT) in the spherical quantum dot with on-center hydrogenic impurity in a four level ladder configuration. The four level ladder configuration is realized by four energy levels of hydrogen impurity: 1S0, 2p−1, 3d−2, and 4f−3, together with the probe and two control laser fields which induce σ− transitions between the given states. Absorption of the probe field as a function of the spherical quantum dot radius and detuning of the probe field is discussed, and comparison of this configuration to the three level ladder configuration is given. Finally, the additional absorption peak that appears in the four level configuration is discussed in detail.

Impurity-modulated Aharonov–Bohm oscillations and intraband optical absorption in quantum dot–ring nanostructures

In this work we study the electronic states in quantum dot–ring complex nanostructures with an on-center hydrogenic impurity. The influence of the impurity on Aharonov–Bohm energy spectra oscillations and intraband optical absorption is investigated. It is shown that in the presence of a hydrogenic donor impurity the Aharonov–Bohm oscillations in quantum dot–ring structures become highly tunable. Furthermore, the presence of the impurity drastically changes the intraband absorption spectra due to the strong controllability of the electron localization type.

Electromagnetically induced transparency in a spherical quantum dot with hydrogenic impurity in the external magnetic field

In this paper we analyzed the realization of the electromagnetically induced transparency (EIT) effect in the spherical quantum dot with on-center hydrogenic impurity under the influence of the external magnetic field. Three energy levels of hydrogen impurity 1s0, 2p−1, and 3d−2, together with the probe and control laser fields, which induce σ− transitions between the given states, form a ladder configuration. Optical Bloch equations for such a system are solved in a stationary regime. Dependence of the susceptibility for such a system on the Rabi frequency of the control field, intensity of the external magnetic field, detuning of the control field, and decay rates coefficients are then discussed in detail. Finally, the explanation in dressed state picture is given.

Group velocity of light in ladder-type spherical quantum dot with hidrogenic impurity

The present paper analyzes the group velocity of light in a ladder-type spherical quantum dot with on-center hydrogenic impurity. The three level ladder configuration is realized by energy levels of hydrogenic impurity, together with the probe and control laser fields. Group velocity of the probe field is then investigated as a function of the spherical quantum dot radius, probe field frequency, and control laser field intensity.

Optical absorption coefficients and refractive index changes of an on-center hydrogenic impurity in a multi-layered spherical quantum dot: effects of external fields and geometrical size

Effects of an on-center hydrogenic impurity, external electric and magnetic fields on the electronic structure, optical absorption coefficients and refractive index changes of a multi-layered spherical quantum dot are investigated. To this end, the direct matrix diagonalization method and the compact density matrix approach are respectively, used to calculate energy eigenvalues and optical properties of the system. It is found that the geometrical size, hydrogenic impurity and external fields change the electronic structure of the system. Therefore, these parameters have a great influence on the linear and the third-order nonlinear optical absorption coefficients as well as the refractive index changes of the system.

Effect of hydrostatic pressure and polaronic mass of the binding energy in a spherical quantum dot

Simultaneous effect of hydrostatic pressure and polaronic mass on the binding energies of the ground and excited states of an on-center hydrogenic impurity confined in a GaAs/GaAlAs spherical quantum dot are theoretically investigated by the variational method within the effective mass approximation. The binding energy is calculated as a function of dot radius and pressure. Our findings proved that the hydrostatic pressure led to the decrease of confined energy and the increase of donor binding energy. Conduction band non-parabolicity and the polaron masses are effective in the donor binding energy which is significant for narrow dots not in the confined energy. The maximum donor binding energy achieved by the polaronic mass in the ground and excited states are 2%–19% for the narrow dots. The confined and donor binding energies approach zero as the dot size approaches infinity.

Effect of geometry on the pressure induced donor binding energy in semiconductor nanostructures

The effect of geometry on an on-center hydrogenic donor impurity in a GaAs /( Ga,Al ) As quantum wire (QWW) and quantum dot (QD) under the influence of Γ–X band mixing due to an applied hydrostatic pressure is theoretically studied. Numerical calculations are performed in an effective mass approximation. The ground state impurity energy is obtained by variational procedure. Both the effects of pressure and geometry are to exert an additional confinement on the impurity inside the wire as well as dot. We found that the donor binding energy is modified by the geometrical effects as well as by the confining potential when it is subjected to external pressure. The results are presented and discussed.

Impurity-related intraband absorption in coupled quantum dot-ring structure under lateral electric field

The effects of a lateral electric field on intraband absorption in GaAs/GaAlAs two-dimensional coupled quantum dot-ring structure with an on-center hydrogenic donor impurity are investigated. The confining potential of the system consists of two parabolas with various confinement energies. The calculations are made using the exact diagonalization technique. A selection rule for intraband transitions was found for x-polarized incident light. The absorption spectrum mainly exhibits a redshift with the increment of electric field strength. On the other hand, the absorption spectrum can exhibit either a blue- or redshift depending on the values of confinement energies of dot and ring. Additionally, electric field changes the energetic shift direction influenced by the variation of barrier thickness of the structure.

Electronic states of coupled quantum dot-ring structure under lateral electric field with and without a hydrogenic donor impurity

A detailed investigation of the lateral electric field effect on single electron states in coupled quantum dot-ring structure has been systematically studied for cases with and without an on-center hydrogenic donor impurity. The single electron energy spectrum has been found using the effective mass approximation and an exact diagonalization technique. The electron ground state's probability density has been examined for different values of the confinement energies and depth of dot confinement relative to the bottom of the quantum ring and barrier thickness. The energy level's dependence on the electric field strength has been studied considering the effects of mentioned parameters of the structure and hydrogenic donor impurity.

The binding energies of a bulged GaAs nanowire

As it is well-known the electronic structure of the semiconductor nanostructures are so sensitive to alteration of confinement while the nanostructure morphology often determines the confinement. Accordingly existence of a bulge on the wire surface will affect the features of the nanowire. In the present work we consider an on-center hydrogenic donor impurity in a GaAs nanowire with bulge. The ground and first excited states energy levels as well as their binding energies are calculated as functions of bulge and nanowire radius. It is found that both the energy levels and binding energies are strongly influenced by the bulge size for ultrafine nanowires. For large wire radii the effects of bulge existence is trivial and the electronic properties of the system approach to those of the simple nanowire.

Binding energy and nonlinear optical properties of an on-center hydrogenic impurity in a spherical quantum dot placed at the center of a cylindrical nano-wire: Comparison of hydrogenic donor and acceptor impurities

The binding energies and corresponding wave functions of ground and first excited states (1s, 2p) of on-center hydrogenic donor and acceptor impurities are calculated using finite difference approximation in the effective mass framework. The on-center impurities are assumed to be in an InAs spherical quantum dot which is located at the center of a GaAs cylindrical nano-wire. To test the validity of applied method the eigenvalues of ground and first excited states are compared with reported results which have been calculated by finite element methods and it is shown that the finite difference approximation is more accurate in this particular case. In addition, the oscillator strength, linear, third-order nonlinear and total optical absorption coefficients and refractive index changes have been calculated for 1s–2p transition by means of the compact density matrix approach. The results show that presence of impurity causes a blue shift in optical spectrum which is larger for acceptor impurity. Also, the amplitude of absorption coefficient, refractive index changes and oscillator strength depend on the absence, presence and type of impurity. Moreover, it is found that the saturation condition can be tuned by type of impurity and critical incident optical intensity is enhanced in presence of acceptor impurity.

Simultaneous effects of external electric field and aluminum concentration on the binding energy of a laser-dressed donor impurity in a spherical quantum dot confined at the center of a cylindrical nano-wire

Based on the effective-mass approximation, the effects of external electric field and laser radiation on the binding energy and Stark shifts of electronic energy levels of a system consist of an on-center hydrogenic donor impurity in a spherical quantum dot which is located at the center of a cylindrical nano-wire have been studied. The energy eigenvalues and corresponding wave functions are calculated using the finite difference approximation. The binding energy and Stark shifts dependencies are reported upon the electric field strength, aluminum concentration and laser radiation. The results reveal that Stark shifts of ground and first excited states are strongly affected by presence of impurity, laser radiation and Al concentration. Additionally, the binding energies decreases as the electric field increases and become negligible for large values of electric field; decreases as the laser radiation increases and increases as the Al concentration increases.

Electron Raman scattering in single and multilayered spherical quantum dots: Effects of hydrogenic impurity and geometrical size

Based on the effective mass and parabolic one-band approximations, the differential cross-section for the intersubband electron Raman scattering process in a single and multilayered spherical quantum dots is investigated. The influence of an on-center hydrogenic impurity and geometrical parameters such as the well and barrier widths on the differential cross-section is studied. Results show that the number, the position and the magnitude of the peaks of emission spectra, considerably depend on the presence of the hydrogenic impurity as well as geometrical parameters. Results also reveal that the magnitude of the peaks significantly depend on the polarization vectors of incident and scattered lights. • Hydrogenic impurity effects on ERS in single and multilayered SQDs are investigated. • Light polarization vectors and geometrical size effects the ERS are also studied. • Number, position and magnitude of the peaks, depend on the presence of the impurity. • The light polarization vectors have a great influence on the magnitude of the peaks. • Geometrical parameters considerably change the peaks number, position and magnitude.

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.