Multilayered Spherical Quantum Dot Research Articles

Optical absorption coefficients of a single electron in a multilayer spherical quantum dot with a Kratzer-like confinement potential

The current study looks at how the Kratzer confinement potential affects the linear, third-order nonlinear, and total optical absorption coefficients (ACs) of a single electron in a multilayered spherical quantum dot (MSQD) by using the finite element method within the effective mass approximation. The variation of the transition energy has been investigated for two allowed transitions, 1p-2s and 2s-2p. Furthermore, we investigated the variation of the linear, third-order nonlinear, and total optical absorption coefficients as a function of the incident photon energy for several transitions while accounting for the effect of the Kratzer confinement potential. The findings show that the optical ACs and transition energy are strongly influenced by the Kratzer confinement potential.

The nonlinear optical rectification and second harmonic generation of a single electron confined in a multilayer spherical quantum dot

The nonlinear optical rectification and second harmonic generation of a single electron confined in a multilayer spherical quantum dot

The impact of the electric field on the photoionization cross section, polarizability, and donor impurity binding energy in multilayered spherical quantum dot

The impact of the electric field on the photoionization cross section, polarizability, and donor impurity binding energy in multilayered spherical quantum dot

Pressure, temperature and electric field effects on the photoionization cross section in a multilayered spherical quantum dot

Pressure, temperature and electric field effects on the photoionization cross section in a multilayered spherical quantum dot

Study of photoionization cross section and binding energy of shallow donor impurity in multilayered spherical quantum dot

In the framework of the effective mass approximation and by using the finite element method , we have studied the simultaneous effects of position dependent effective mass (PDEM) and dielectric function on the shallow donor impurity binding energy and photoionization cross section in a multilayered spherical quantum dot . We have also investigated the influence of conduction band nonparabolicity and polaronic mass on the both binding energy and photoionization cross section (PCS). The obtained results have shown that the nonparabolicity and polaronic mass effects enhance the binding energy and photoionization cross section. Furthermore, it can be concluded from this research that the binding energy and the PCS are strongly dependent on the geometrical parameters, and PDEM. Changes in binding energy and photoionization cross section have physical reasons, which are discussed in details. • The photoionization cross section (PCS) and the binding energy are strongly dependent on the width of the structure layers. • The conduction band nonparabolicity and the polaronic mass effects enhance the binding energy and reduce the PCS peak magnitude. • The dependence of the dielectric function ε ( r ) on the electron coordinates makes the amplitude peak of the PCS take high values.

Investigation of the nonlinear optical rectification coefficient in a multilayered spherical quantum dot

In the framework of the effective mass approximation, we have investigated the effects of hydrostatic pressure, temperature, nonparabolicity of the band, and polaronic mass on nonlinear optical rectification. Furthermore, the optical rectification coefficient's dependency on the inner dot radius and the barrier width is also investigated. The obtained results reveal that geometrical sizes, hydrostatic pressure, and temperature all have a significant impact on the nonlinear optical rectification. Moreover, the combined effects of the conduction band nonparabolicity and polaronic mass produce a redshift of the peak position and a reduction in the resonant peak magnitude.

Hydrostatic pressure, temperature, and electric field effects on the hydrogenic impurity binding energy in a multilayered spherical quantum dot

Hydrostatic pressure, temperature, and electric field effects on the hydrogenic impurity binding energy in a multilayered spherical quantum dot

Impurity photoionization cross-section and intersubband optical absorption coefficient in multilayer spherical quantum dots

Energy spectrum, wave functions and binding energies of the electron to the donor impurity ion located in the center of a multilayer spherical quantum dot (MSQD) consisting of a core and two spherical shells were studied within the effective mass approximation. Based on the exact wave functions of the electron expressed in terms of Coulomb functions of the first and second kind, the spectral dependences of the photoionization cross section of the impurity (PCS) and the intersubband optical absorption coefficient (OAC) for various geometric dimensions of the nanostructure were calculated. It is shown that the decrease in the width of the external potential well changes the localization of the electron in the nanosystem which significantly affects the binding energy of the electron with the impurity, photoionization cross section and interband absorption coefficient. The position of the PCS peak associated with the quantum transition of an electron from the ground state to the 1p0 state shifts to the region of higher energies, and its height decreases. At the same time, the height of PCS peaks associated with quantum transitions to higher excited states (2p0, 3p0) increases.The presence of impurities and changes in the MSQD size significantly affect the intersubband absorption coefficient. Decrease of the external potential well width in the absence of impurities leads to a monotonous increase in OAC through the first excited state, and in the presence of a central impurity, absorption through states with higher energy increases.

Variations of non-linear optical properties and susceptibility with layer thicknesses of CdS/ZnS/CdS/ZnS multilayer quantum dot

Susceptibility determines the linear and non-linear optical nature of a material, by defining the response of material to the electric field of light. Being a material parameter, susceptibility must change with the size and shape of the material in the nano regime. Implementing the effective mass approximation, we studied the role of susceptibility on the linear and non-linear absorption of CdS/ZnS/CdS/ZnS multilayer spherical quantum dot. Our results show that susceptibility is the key parameter that determines the non-linear optical absorption properties, both in inter-band and intra-band absorption, of multilayer quantum dot. Thus by tuning the susceptibility through varying layer thickness, we can control the non-linear behavior of the nano-heterostructure.

Electromagnetically induced transparency in a multilayered spherical quantum dot with hydrogenic impurity

In this paper the effects of size, hydrostatic pressure and temperature on electromagnetically induced transparency, as well as on absorption and the dispersion properties of multilayered spherical quantum dot with hydrogenic impurity are theoretically investigated. Energy eigenvalues and wavefunctions of quantum systems in three-level and four-level configurations are calculated using the shooting method, while optical properties are obtained using the density matrix formalism and master equations. It is shown that peaks of the optical properties experience a blue-shift with increasing hydrostatic pressure and red-shift with increasing temperature. The changes of optical properties as a consequence of changes in barrier wells widths are non-monotonic, and these changes are discussed in detail.

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.

Quadratic Electro-Optic Effect and Electro Absorption Process of Multi-layer Spherical Quantum Dot Enhanced by Metal Nanoparticle

In this work, the quadratic electro-optic effects (QEOE) and electro-absorption (EA) process of hybrid structure consisting of metal nanoparticle (MNP) coupled to multi-layer spherical quantum dot (MSQD) are investigated numerically. The energy levels and corresponding wave functions of Schrodinger equation in the effective mass approximation are obtained using the fourth-order Runge-Kutta method. The effect of MNP in the vicinity of MSQD is calculated by considering local field enhancement. Then, the variation of QEOE and EA process of hybrid system is reported. The results show that the presence of MNP near MSQD enhances the optical nonlinearity. Also, by changing the parameters such as distance between MNP and MSQD, and radius of MNP, the variations of optical nonlinearity are studied.

Spin–orbit interaction in a multilayered spherical quantum dot

The conventional spin–orbit interaction due to the presence of a central or off-central impurity located in a multilayered spherical quantum dot (MSQD) has been investigated. The different effective masses of dots and barriers have been taken into consideration. The spin–orbit interaction has been calculated in the excited state (2p). The variational method has been applied by using a new form of the trial wave function in addition to the conventional form that has been used in previous work. The new form has the advantage of satisfying the boundary conditions at the interfaces between dots and barriers in the case of different masses. The case of central impurity has been further explored by using the exact analytical solution in the state (2p) of the radial Schrodinger equation in the presence of the impurity. Moreover, the calculations have been performed in the case of a MSQD of thin inner barrier, for which the electron is most probably localized in the outer dot. Thus for an off-central impurity placed in the inner dot the spin–orbit energy increases continuously as the impurity location moves towards the surface of the inner dot. The study has yielded new analytical expressions for the electron energy, binding energy and spin–orbit expectation energy for both central and off-central impurities.

The effect of metal nano particle on optical absorption coefficient of multi-layer spherical quantum dot

In this paper, we investigate the optical absorption coefficient of hybrid structure consisting of metal nano particle (MNP) coupled to multi-layer spherical quantum dot (MSQD). Energy eigenvalues and eigenfunctions of Schrödinger equation in this structure are obtained by using numerical solution (by the fourth-order Runge–Kutta method). The effect of MNP in the vicinity of MSQD is calculated by considering local field theory. Then the variation of optical absorption coefficient hybrid structure is calculated. The results show that the presence of MNP near MSQD enhances the optical absorption coefficient. Also, by changing the distance between MNP and MSQD and radius of MNP, variation of optical absorption coefficient and refractive index changes are introduced.

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.

Nano multi-layered spherical quantum dot optimization by PSO algorithm: Maximizing the optical absorption coefficient

In this paper, the maximization of optical absorption coefficient of multi-layer spherical quantum dot (MSQD) has been investigated based on particle swarm optimization (PSO) method. By using this method and numerical solution of Schrödinger equation (energy eigenvalues and eigenvectors are calculated using the fourth-order Runge–Kutta method), optimal MSQD structure has been determined to maximise the optical absorption coefficient. Having introduced the optimal structure, the refractive index changes and effects of pressure and temperature on the optical absorption coefficient of this structure have been studied. The result shows that the maximum total optical absorption coefficient for the optimal structure is equal to 1.33×105m-1 and its sensitivity dependence to changes of the first well width is more than that of other parameters.

Numerical simulation and time-dependent quantum analysis of electron properties in multilayer spherical InGaAs/AlGaAs quantum dot

In this paper, the time-dependent numerical simulation of multilayer spherical InGaAs/AlGaAs quantum dot (MSQD) based on wave nature of electrons has been presented. The properties of the system solution of the time-dependent Schrödinger coupled with the Poisson equations have been self-consistently solved and the Hartree and exchange-correlation potentials as well as the penetration of wave function in the barrier regions have been calculated. By applying quantum mechanics laws on multilayer spherical quantum dot the electron density, potential energy and current density of system have been analyzed. Calculations show that a small density of carriers penetrates into the classically forbidden regions of the barriers for a finite distance while the majority of density of carriers accumulates away from the barriers in the reservoir. The results show due to boundary effects the time evolution of the current density in the close system grows into a non-realized physical behavior.

The photoionization cross section of a hydrogenic impurity in a multi-layered spherical quantum dot

In this study, we have investigated the photoionization cross section of an on-center hydrogenic impurity in a multi-layered spherical quantum dot. The electronic energy levels and their wave functions have been determined fully numerically by shooting method. Also, we have calculated the binding energy of the impurity by using these energy values. The photoionization cross section has also been computed as a function of the layer thickness and normalized photon energies. We have discussed in detail the possible physical reasons behind the changes in the binding energies and photoionization cross section. It is observed that both the binding energies and the photoionization cross sections depend strongly on the layer thickness and photon energies.

The electronic properties of a core/shell/well/shell spherical quantum dot with and without a hydrogenic impurity

In this study, we have performed a detailed investigation of the electronic properties of a core/shell/well/shell multilayered spherical quantum dot, such as energy eigenvalues, wave functions, electron probability distribution, and binding energies. The energy eigenvalues and their wave functions of the considered structure have been calculated for cases with and without an on-center impurity. For this purpose, the Schrödinger equation has been numerically solved by using the shooting method in the effective mass approximation for a finite confining potential. The electronic properties have been examined for different core radii, barrier thicknesses, and well widths in a certain potential. The results have been analyzed in detail as a function of the layer thicknesses and their physical reasons have been interpreted. It has been found that the electronic properties are strongly dependent on the layer thicknesses.

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.