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In this study, we have investigated theoretically the third-order nonlinear susceptibility associated with intersubband transition in a GaN/GaN/InxGa1−xN/GaN quantum dot-quantum well (QD-QW) structure, emphasizing the influence of the shell thickness, indium concentration and applied electric field F. The wave functions and eigenenergies of confined electrons have been theoretically computed under the effective mass approximation and the compact matrix density. The numerical result show that the intensity and position peak of susceptibility are considerably affected by the geometrical parameters, the applied electric filed and the indium concentration. The result of this work can be used in fabrication of electronic and photonic devices. [ABSTRACT FROM AUTHOR]

• Intersubband transition in elliptical cylindrical CdS/ZnS core/shell quantum dots. • The Photoionization cross-section is investigated with several capped matrices. • The binding energy affected by the electric field intensity, the degree of ellipticity and the immersed matrix. In this study, the effects of the electric field in different directions on hydrogenic donor impurity (HDI) confined to a CdS/ZnS elliptical core/shell cylindrical quantum dot (ECSCQD) immersed in a dielectric matrix (DM) were investigated. The binding energy (BE) and their corresponding photoionization cross-section (PICS) are computed by solving the Schrödinger equation in cylindrical coordinates in the framework of the effective mass approximation (EMA) using a variational and perturbation approach. The effects of different dielectric matrices, lateral and normal electric field (EF) force, geometric factors such as the size of ECSCQDs and ellipticity constants on BE and PICS were presented. It has been indicated that weak lateral EF strength compared to normal EF strength, dielectric matrix, and geometric factors have a significant effect on the BE and PICS. In addition, it was observed that dielectric matrices and different ellipticity constants were quite effective on the Stark shift (S.S.) in the hydrogenic donor impurity ground state energy due to the electric field. The results obtained from the calculations showed that the structure factors, different impurity positions, the external electric field applied to the structure, the elliptical cylinder shape and the dielectric matrix in which the structure is embedded are quite decisive in the magnitude of the PICS amplitudes and resonant peak values. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of CdSe/ZnSe semiconductor core/shell quantum dots with hydrogenic donor impurity were investigated theoretically. The perturbation approach and variational method were used in calculations under Effective Mass Approximation. The considered structure is embedded in a variable polymer matrix. The binding energy (BE), photoionization cross-section, polarizability, and diamagnetic susceptibility of the excited impurity were calculated first according to the core/shell radius ratio and then under a significant external electric field and in the absence of an external electric field. A significant stark shift was observed in the BE relative to the embedded matrix element. [ABSTRACT FROM AUTHOR]

A new investigation on photo-ionization cross section (PICS) of a donor impurity confined in a GaAs/AlGaAs core/shell elliptic quantum dots (CSEQDs) has been performed under electric field (EF) effect. By means of the finite element method (FEM), we have computed the binding energy (BE), oscillator strength P i f and PICS within the framework of the effective mass theory (EMT). Our numerical results reveal that the stark shift is greatly dependent on the strength of the EF, the degree of ellipticity β , and the states of electronic transitions. It can take positive or negative values depending on the situation. In addition, the photo-ionization describing the transition from the donor impurity ground-state (1 s i m p ) to one of the conduction sub-band states (1 s 0 , 2 s 0 , and 2 p 0 ) is affected by the shape of the quantum dots (QDs) and the EF. We demonstrated that varying internal and external parameters may control the photo-ionization cross-section. These characteristics can be exploited to fabricate optoelectronic devices like QD infrared photodetectors. [Display omitted] • The ground, the first and second excited states binding energies of on-center impurity are affected by the EF. • The dependence of the Stark shift of three low-lying electron transition states with on-center impurity on the electric field present a symmetric contribution. • The peaks of PICS are strongly affected by the EF and the shapes of GaAs/AlGaAs CSEQDs. • The prolate "CSEQD" shape has the strongest PICS amplitude of the 1 s i m p - 2 p 0 transition, with a notable blue-shift for this transition. • We recommend that future theoretical and experimental work focus on core–shell prolate QDs because the PICS have a higher magnitude in this case. [ABSTRACT FROM AUTHOR]

• Binding energy in Ge/siGe and in its inverted embedded in oxide matrix structure was investigated. • The Stark Shift is studied with the effect of surrounding matrix and applied electric field. • PICS Ge/SiGe and SiGe/Ge are more pronounced with the change of the geometric parameters, EF intensity and encapsulated matrix. In this study, the binding energy (BE) and photoionization cross-section (PICS) coefficients in a Ge/Si 0.15 Ge 0.85 core/shell quantum dots (CSQDs) and in its inverted structure Si 0.15 Ge 0.85 / Ge (ICSQDs) are studied. The influence of the hydrogenic impurity and capped matrix are taken into account. The electronic states and their related eigenfunctions are computed by solving the three-dimensional Schrödinger equation under the framework of the effective mass approximation (E.M.A) using the variational dimensional. The influence of the core radius and electric field strength on the BE and PICS are investigated. The numerical results reveal that the optoelectronic properties are considerably affected by the electric field strength (EF), immersed oxide matrix (OM) and geometric parameter. The obtained results prove that the PICS magnitude increases as the core radius increases and its resonant peak moves towards the lower energies for Ge/Si 0.15 Ge 0.85 CSQDs structure, and increases as the core radius decreases and its resonant peak experiences a blue shift with increasing core radius for Si 0.15 Ge 0.85 / Ge ICSQDs. Moreover, with the effects of the surrounding oxide matrix and electric field strength, the PICS magnitude is improved and their resonant peak suffers a redshift. [ABSTRACT FROM AUTHOR]

This work presents a theoretical analysis of a CdTe/CdS core/shell quantum dots embedded in a dielectric oxide matrix under the influence of hydrogenic impurity and the applied electric field intensity. The eigenstates and their corresponding eigenfunctions are computed by solving the Schrodinger equation using the finite element method within the effective mass approximation. The first-order linear and third-order nonlinear optical absorption coefficients as well as the refractive index changes are computed based on the compact density matrix approach. The obtained result shows that the first-order linear and third-order nonlinear optical properties are more pronounced with the electric field, surrounding oxide matrix and the donor impurity effects. However, the first-order linear and third-order nonlinear optical absorption coefficients and refractive index changes can experience a red or blue shift under the influence of electric field, oxide matrix and hydrogenic impurity. In addition, under all conditions, the height peaks of these optical properties can be raised (fall). Our findings demonstrate the critical importance of considering the roles of electric field, the presence of donor impurity, and the capped dielectric oxide matrix in the design and fabrication of core–shell-based optoelectronic devices. • The presence of the emergent TiO 2 oxide matrix (OM) significantly improves the peak values of the optical properties compared to other OM or isolated quantum dots. • The application of an external electric field affects the absorption coefficient differently depending on the nature of the transition. • The presence of a hydrogen-confined impurity causes a blue-shift of the peak absorption coefficient. [ABSTRACT FROM AUTHOR]

In this review, we have investigated theoretically the third-order nonlinear optical susceptibility in Ge/Si 0.15 Ge 0.85 spherical core/shell quantum dots under electric field (EF) for both cases with and without on-center impurity within the framework of the compact-density-matrix (C.D.M). The eigenenergies and their corresponding wave functions of the system are computed by solving the three-dimensional Schrödinger equation using the effective mass approximation (E.M.A) using the variational method (VM). Our computational results show that both the energy levels and the third-order nonlinear optical susceptibility are strongly affected by the quantum dot size, the effects of the hydrogenic impurity, and the electric field intensity. • The hydrogenic impurity effect in Ge/Si 0.15 Ge 0.85 spherical CSQDs under an EF. • The Realχ(3) and the Imχ(3) are examined with the applied EF intensity. • The third-order nonlinear optical susceptibility is investigated with the QDs size. [ABSTRACT FROM AUTHOR]

The current work describes in detail the effect of polarization charges on the electronic properties of core/shell spherical quantum dots (CSQDs) structures composed of CdTe/ZnTe semiconductors. In the calculations, energy levels and wave functions matching these levels were calculated by using the effective mass approach (EMA). Furthermore, the binding energy of a hydrogenic impurity was calculated under the variational approach. The matrix effects surrounding the CSQDs structure, the quantum dot size, the impurity, and how the applied external electric field affects the impurity binding energy (E b), polarizability (P a) and photoionization cross-section (PICS) are calculated and discussed in detail. The obtained results revealed that the E b , the PICS and P a are not only affected by the quantum parameter size but also by the capped matrix, the impurity and external electric field EF actions. • Ground state binding energy in CdTe/ZnTe CSSQD. • Stark shift and polarizability have been studied under the effects of the electric field and the surrounding matrix. • Peaks of photoionization cross-section experienced a red shift with the appropriate dielectric environment. [ABSTRACT FROM AUTHOR]

The features of electron-impurity polarizability in a quantum nanostructure are investigated from the knowledge of allowed electron states coupled to a shallow-donor impurity. The influence of geometry on the carrier confinement and the presence of external probes such as electric fields are explicitly considered. For the sake of illustration, the example of CdS/ZnSe-based prolate ellipsoidal core/shell quantum dot (PECSQD) configuration is chosen. This problem allows to consider a finite confinement potential model, employing both the finite element method and the effective mass approximation. Within this framework, impurity-related energies and associated polarizability for the lowest states were determined as functions of the shell thickness, core dimensions, impurity position, and applied electric field strength - while keeping the shell dimensions fixed. Electron-impurity energies are largely affected by electric field values. Under thinner shell conditions, polarizability shows variations with field strength that include "anomalous" negative values for certain states. Then, the increase in shell thickness causes a significant increment in the polarizabilities, regardless impurity position. • Electronic properties in prolate ellipsoidal core/shell quantum dots. • Effects of a shallow donor impurity. • Influence of externally applied electric field. • Calculation of electron-impurity polarizability for different allowed states. • Appearance of negative values of polarizability for certain excited states. [ABSTRACT FROM AUTHOR]