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The role of strain in material properties is well-established, serving as a tool for altering atomic positions and defect formation, adjusting electronic structures and lattice vibrations, and influencing phase transitions, physical characteristics, and chemical properties. In this study, we conducted theoretical calculations of the binding energy and photoionization cross section (PCS) within a spherical core/shell quantum dot (CSQD) for the different transitions between the ground state of a donor impurity and the four low-lying conduction band states. During our study, we employed the finite element method to determine the energy levels and wave functions of the system within the effective mass approximation. Subsequently, we investigated the changes in PCS and binding energy while varying shell width under the influence of an applied electric field, considering both cases with and without the effect of strain. The strain effect was incorporated based on Hooke's law, and we developed specific expressions and utilized the continuum linear elasticity mechanical model for a single spherically symmetric shell. The results demonstrate that the strain correction enhances the binding energy of the four low-lying energy levels, leading to a shift of the PCS peaks toward higher energies. Conversely, the application of an external electric field has varying effects depending on the specific transition being considered. We compared our theoretical results with available experimental data and found them to be in good agreement. The pronounced blue-shift and substantial enhancement in magnitude of PCS spectra concerning shell width, electric field, and strain make CSQDs highly promising candidates for applications in adjustable nano-optoelectronic devices. [ABSTRACT FROM AUTHOR]

This study employs the finite element method based on the effective-mass approximation (EMA) to numerically investigate the behavior of impurities in multilayer cylindrical quantum dots (MLCQDs). We consider the applied hydrostatic pressure (P) in our numerical analysis. The study presents numerical results for macroscopic parameters that follow the electronic properties, the binding energy (Eb), and diamagnetic susceptibility (χdia) of the ground state (1 s) and some excited states (1p and 2 s) of the impurity in the MLCQDs. The Eb and the χdia for the three states are calculated as a function of the radius R , impurity position z 0 and the hydrostatic pressure. The numerical results show that the binding energies of impurities decrease with the radius for all levels. The E b 1 s and E b 1 p have three maximum values that typify the number of the quantum dot layer materials contained in our system. Moreover, the diamagnetic susceptibility for the three levels is strongly affected by the hydrostatic pressure, impurity location, and radius. [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]

This study systematically explored the binding energy and the photoionization cross-section (PCS) of a hydrogenic shallow donor impurity within a GaAs double quantum box structure incorporated into a Ga (1 − x) Al x As matrix under the influence of an external intense magnetic field. The computations are performed using the effective-mass approximation (EMA) and the finite element method (FEM), taking into account a finite potential across all surfaces of the nanosystem. The results emphasize the significant role of the magnetic field, primarily in enhancing the donor binding energy within the double quantum box system. We demonstrate that increasing the magnetic field results in an augmentation of binding energy across various aluminum concentrations. The PCS of a shallow donor impurity undergoes a blue shift when shifted from the barrier center to the box center, attributed to the increased binding energy. When the double quantum box is subjected to a magnetic field effect, the amplitude peaks of PCS show an elevation coupled with a blue shift. By setting magnetic field values at 0 T, 35 T, or 70 T and varying aluminum concentrations, we observe a shift in the PCS towards higher energy levels along with an increase in peak amplitude. We also study the PCS of the donor impurity as a function of photon energy, mainly examining the effects of box width and barrier width modifications in the double quantum box. [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]

This study delves into the optical characteristics of multilayered spherical quantum dots (MLSQDs). By employing the finite element method, we systematically explore the impact of varying layer dimensions, the A l -concentration, and the intersubband relaxation time on the linear, third nonlinear, and total optical absorption coefficients and refractive index changes within this nanostructure. Our findings reveal intriguing correlations between the sizes of individual layers and the resultant optical responses. Notably, subtle adjustments in layer dimensions manifest profound changes in both linear and third-order nonlinear absorption coefficients. Furthermore, the investigation of relaxation time elucidates the key role it plays in changing optical properties, illustrating how relaxation time influences the optical behavior of MLSQDs. This study provides a comprehensive understanding of the impact of layer sizes, relaxation time, and A l concentration on the optical properties of MLSQDs. These findings offer valuable guidance for engineering customized optical functionalities in nanophotonic technologies. • The OAC peaks shift red with increased core radius, then blue shifts at larger sizes. • The OACs and RICs generally follow the trends observed in the transition energy. • Higher relaxation times lead to stronger and sharper absorption peaks. • A l -concentration is another dimension to the control and tuning of QD properties.. [ABSTRACT FROM AUTHOR]

GaAs/GaAlAs quantum dots can be doped with various impurities to modify their optoelectronic properties. Common impurities used for doping include: Hydrogenic impurity (HI), Silicon (Si), Selenium (Se), Germanium (Ge), and Sulfur (S) are common n-type dopant in GaAs-based materials. This work has investigated the effects of temperature and pressure on the refractive index changes (RICs) and optical absorption coefficients (OACs) in the multi-layer quantum disk, accounting for central cell correction. We have used the finite element method to calculate the eigenvalues and their corresponding wave-functions. These values are utilized in the computation of the OACs and RICs. Our outcomes can be summarized as follows: (i) The applied pressure induces a red-shift of the OACs peaks, and their magnitude is reduced. Similarly, temperature causes a blue-shift of the OACs peaks, and their magnitude is enhanced. (ii) The presence and type of impurity lead to significant changes in both OACs and RICs. • The pressure induces a red-shift of the OACs peaks, and their magnitude is reduced. • Temperature causes a blue-shift of the OACs peaks, and their magnitude is enhanced. • The presence and type of impurity lead to significant changes in both OACs and RICs. • Different impurity atoms significantly impact the opto-electronic properties of MLQD. [ABSTRACT FROM AUTHOR]