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To achieve n-type doping in diamond, extensive investigations employing first principles have been conducted on various models of phosphorus doping and boron–phosphorus co-doping. The primary focus of this study is to comprehensively analyze the formation energy, band structure, density of states, and ionization energy of these structures. It is observed that within a diamond structure solely composed of phosphorus atoms, the formation energy of an individual carbon atom is excessively high. However, the P-V complex substitutes 2 of the 216 carbon atoms, leading to the transformation of diamond from an insulator to a p-type semiconductor. Upon examining the P-B co-doped structure, it is revealed that the doped impurities exhibit a tendency to form more stable cluster configurations. As the separation between the individually doped atoms and the cluster impurity structure increases, the overall stability of the structure diminishes, consequently resulting in an elevation of the ionization energy. Examination of the electronic density of states indicates that the contribution of B atoms to the impurity level is negligible in the case of P-B doping. [ABSTRACT FROM AUTHOR]

The results of theoretical calculations of electronic states of the gallium oxide (Ga2O3) nanocrystals both doped with donor impurity and undoped have been presented in the paper. In the envelope function approximation, the structure, states and energy levels of size quantization in the nanocrystals were determined. According to our calculations, the electron-hole pair forms a bound state of the exciton type in the nanocrystal. The typical donor impurities in Ga2O3, such as silicon and tin, were shown to create bandgap states localized in a spatial domain being several times smaller than the nanocrystal’s volume. Forming a compact neutral pair, the electron and donor ions have no noticeable influence on the states of the optically excited electron-hole pairs. The effect of impurity implantation on recombination processes was also discussed.

To achieve n-type doping in diamond, extensive investigations employing first principles have been conducted on various models of phosphorus doping and boron–phosphorus co-doping. The primary focus of this study is to comprehensively analyze the formation energy, band structure, density of states, and ionization energy of these structures. It is observed that within a diamond structure solely composed of phosphorus atoms, the formation energy of an individual carbon atom is excessively high. However, the P-V complex substitutes 2 of the 216 carbon atoms, leading to the transformation of diamond from an insulator to a p-type semiconductor. Upon examining the P-B co-doped structure, it is revealed that the doped impurities exhibit a tendency to form more stable cluster configurations. As the separation between the individually doped atoms and the cluster impurity structure increases, the overall stability of the structure diminishes, consequently resulting in an elevation of the ionization energy. Examination of the electronic density of states indicates that the contribution of B atoms to the impurity level is negligible in the case of P-B doping.

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]

We calculate energies of shallow donors confined in a rolled-up quantum well in the presence of the electric field by solving numerically the Schrödinger equation in natural curvilinear coordinates. It is found that the curves of density of states (DOSs) are very sensitive to the variation of the donor position, the geometry of the spiral and the applied electric field value. Novel results for dependencies of donor's dipole moment and its polarizability on the electric field strength and its orientation, for different donor positions are presented. Additionally, we found that the anisotropic Stark effect of the first order provides in this structure a dependency of the polarizability on the external electric field in a spike-like shape, giving rise to a sharp variation of the dipole moment. [ABSTRACT FROM AUTHOR]

This study investigates the effect of quantum size and an external magnetic field on the optoelectronic properties of a cylindrical Al x Ga 1 − x As/GaAs-based core/shell nanowire. We used the one-band effective mass model to describe the Hamiltonian of an interacting electron-donor impurity system and employed two numerical methods to calculate the ground state energies: the variational and finite element methods. With the finite confinement barrier at the interface between the core and the shell, the cylindrical symmetry of the system revealed proper transcendental equations, leading to the concept of the threshold core radius. Our results show that the optoelectronic properties of the structure strongly depend on core/shell sizes and the strength of the external magnetic field. We found that the maximum probability of finding the electron occurs in either the core or the shell region, depending on the value of the threshold core radius. This threshold radius separates two regions where physical behaviors undergo changes and the applied magnetic field acts as an additional confinement. [ABSTRACT FROM AUTHOR]

In the model of effective masses and rectangular potentials, the effect of a hydrogen-like donor impurity on the energy spectrum, electron wave functions and oscillator strengths of intraband quantum transitions in a quantum dot–quantum ring semiconductor nanostructure (GaAs/AlxGa1-xAs) is studied theoretically. The stationary Schrödinger equation for an electron interacting with an impurity cannot be solved analytically exactly. For its approximate solution, the unknown wave functions are sought in the form of an expansion over a complete set of cylindrically symmetric wave functions in the nanostructure without impurity, and the electron energy is found by solving the corresponding secular equation. The dependences of the energy spectrum, the binding energy of the electron with the impurity and the oscillator strengths of the quantum intraband transitions on the geometric parameters of the nanostructure are analyzed. [ABSTRACT FROM AUTHOR]

A theoretical analysis of optical properties in a ZnS/CdS/ZnS core/shell/shell spherical quantum dot was carried out within the effective mass approximation. The corresponding Schrödinger equation was solved using the finite element method via the 2D axis-symmetric module of COMSOL-Multiphysics software. Calculations included variations of internal dot radius, the application of electric and magnetic fields (both oriented along z-direction), as well as the presence of on-center donor impurity. Reported optical properties are the absorption and relative refractive index change coefficients. These quantities are related to transitions between the ground and first excited states, with linearly polarized incident radiation along the z-axis. It is found that transition energy decreases with the growth of internal radius, thus causing the red-shift of resonant peaks. The same happens when the external magnetic field increases. When the strength of applied electric field is increased, the opposite effect is observed, since there is a blue-shift of resonances. However, dipole matrix moments decrease drastically with the increase of the electric field, leading to a reduction in amplitude of optical responses. At the moment impurity effects are activated, a decrease in the value of the energies is noted, significantly affecting the ground state, which is more evident for small internal radius. This is reflected in an increase in transition energies. [ABSTRACT FROM AUTHOR]

This article presents a theoretical study of the electronic, impurity-related, and nonlinear optical properties of CdS/ZnS quantum dots subjected to electric and magnetic fields. The magnetic field is applied along the z-axis, with the donor impurity always located in the center of the quantum dot. In the case of the electric field, two situations have been considered: applied along the z-axis and applied in the radial direction (central electric field). In both cases, the azimuthal symmetry (around the z-axis) is preserved. In the absence of a magnetic field and considering a central electric field, the system preserves its spherical symmetry both in the presence and in the absence of the donor impurity. The study is carried out in the effective mass approximation and it uses the finite element method to find the eigenfunctions and their corresponding energies, both in the presence and in the absence of the impurity. This work investigates the optical absorption coefficient and the relative change of the refractive index, considering only intraband transitions between l = 0 states (states with azimuthal symmetry concerning the z-axis). Calculations are for z-polarized incident radiation. The study shows that the combined effects of a central electric field and a z-directed magnetic field can give rise to a typical core/shell-like quantum confinement with oscillations of the electron ground state. Additionally, it is shown that the presence of the donor impurity suppresses such oscillations and it is responsible for blue shifts in the optical properties and magnifications of the corresponding resonances. [ABSTRACT FROM AUTHOR]

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.

Using a variational method in the effective mass approximation, we calculated the binding energy and polarisation of a shallow donor in a GaAs-Ga1-xAlxAs pillbox surrounded by Ga1-yAlyAs. We present our results as a function of the impurity positions and the strength of the electric field for different shapes of the pillbox with constant volume. It is found that the binding energy and polarisation of donor impurity depend strongly on the shape of the pillbox, the position of the impurity, the intensity of the electric field and the thickness of the potential barrier. [ABSTRACT FROM AUTHOR]

The optical absorption of the donor impurity in the two-dimensional GaAs quantum ring was studied with the effective mass approximation using the finite element method. The influence of the magnetic field, light intensity, and impurity position on the optical absorption coefficient is analyzed. The results reveal that the application of a magnetic field can increase the peak value of the absorption coefficient and cause a blue shift phenomenon. With the increase of light intensity, the peak splitting in total optical absorption appears. With the increase of the distance between the impurity and the center of the quantum ring, the spacing of the energy level decreases, resulting in a decrease in the peak value of the total absorption coefficients, and a red shift occurs. On the other hand, when the impurity is located between the inner and outer radius, the opposite effects appear as the impurity is far from the center of the quantum ring. [ABSTRACT FROM AUTHOR]

We calculate energies of shallow donors confined in a rolled-up quantum well in the presence of the electric field by solving numerically the Schrödinger equation in natural curvilinear coordinates. It is found that the curves of density of states (DOSs) are very sensitive to the variation of the donor position, the geometry of the spiral and the applied electric field value. Novel results for dependencies of donor’s dipole moment and its polarizability on the electric field strength and its orientation, for different donor positions are presented. Additionally, we found that the anisotropic Stark effect of the first order provides in this structure a dependency of the polarizability on the external electric field in a spike-like shape, giving rise to a sharp variation of the dipole moment.

This study investigates the effect of quantum size and an external magnetic field on the optoelectronic properties of a cylindrical AlxGa1−xAs/GaAs-based core/shell nanowire. We used the one-band effective mass model to describe the Hamiltonian of an interacting electron-donor impurity system and employed two numerical methods to calculate the ground state energies: the variational and finite element methods. With the finite confinement barrier at the interface between the core and the shell, the cylindrical symmetry of the system revealed proper transcendental equations, leading to the concept of the threshold core radius. Our results show that the optoelectronic properties of the structure strongly depend on core/shell sizes and the strength of the external magnetic field. We found that the maximum probability of finding the electron occurs in either the core or the shell region, depending on the value of the threshold core radius. This threshold radius separates two regions where physical behaviors undergo changes and the applied magnetic field acts as an additional confinement.

Nanoflakes ultra-thin quantum dots are theoretically studied as innovative nanomaterials delivering outstanding results in various high fields. In this work, we investigated the surface properties of an electron confined in spherical ultra-thin quantum dots in the presence of an on-center or off-center donor impurity. Thus, we have developed a novel model that leads us to investigate the different nanoflake geometries by changing the spherical nanoflake coordinates (R, α , ϕ). Under the infinite confinement potential model, the study of these nanostructures is performed within the effective mass and parabolic band approximations. The resolution of the Schrödinger equation is accomplished by the finite difference method, which allows obtaining the eigenvalues and wave functions for an electron confined in the nanoflakes surface. Through the donor and electron energies, the transport, optoelectronic, and surface properties of the nanostructures were fully discussed according to their practical significance. Our findings demonstrated that these energies are more significant in the small nanoflakes area by altering the radius and the polar and azimuthal angles. The important finding shows that the ground state binding energy depends strongly on the geometry of the nanoflakes, despite having the same surface. Another interesting result is that the presence of the off-center shallow donor impurity permits controlling the binding energy, which leads to adjusting the immense behavior of the curved surface nanostructures. [ABSTRACT FROM AUTHOR]

A theoretical analysis of optical properties in a ZnS/CdS/ZnS core/shell/shell spherical quantum dot was carried out within the effective mass approximation. The corresponding Schrödinger equation was solved using the finite element method via the 2D axis-symmetric module of COMSOL-Multiphysics software. Calculations included variations of internal dot radius, the application of electric and magnetic fields (both oriented along z-direction), as well as the presence of on-center donor impurity. Reported optical properties are the absorption and relative refractive index change coefficients. These quantities are related to transitions between the ground and first excited states, with linearly polarized incident radiation along the z-axis. It is found that transition energy decreases with the growth of internal radius, thus causing the red-shift of resonant peaks. The same happens when the external magnetic field increases. When the strength of applied electric field is increased, the opposite effect is observed, since there is a blue-shift of resonances. However, dipole matrix moments decrease drastically with the increase of the electric field, leading to a reduction in amplitude of optical responses. At the moment impurity effects are activated, a decrease in the value of the energies is noted, significantly affecting the ground state, which is more evident for small internal radius. This is reflected in an increase in transition energies.

The effect of the magnetic field on the electron states in the Al 0.3 Ga 0.7 As/GaAs/Al 0.3 Ga 0.7 As multilayered quantum dot with and without shallow-donor impurity is under study. The magnetic field dependence of the impurity-related transition energies and the corresponding photoionisation cross-section is calculated, taking into account the excited states. The problem is solved using the effective mass approximation and rectangular potential profiles for wells and barriers using diagonalisation and finite element methods. The results obtained by both methods coincide with high accuracy. It is shown that the transition energies and photoionisation cross-section strongly depend on the impurity position and the magnetic field induction. As the magnetic field induction increases, all the peaks of photoionisation cross-section shift to the region of higher energies in the case of off-centre impurity and shift to lower energies in the case of on-centre impurity. The effect of merging two photoionisation cross-section peaks with increasing magnetic field induction is revealed, leading to a significant increase in the value of impurity photoionisation cross-section. [ABSTRACT FROM AUTHOR]

In this study, linear, nonlinear and total optical absorption coefficients related a single shallow donor atom confined in semiconductor core/shell/shell quantum dot heterostructure are researched in detail within the compact density matrix formalism approximation. For this purpose, firstly, the energies and the wavefunctions are computed by the diagonalization method in the effective mass approach. Moreover, the effects of size modulation, donor position and magnetic field are analyzed. The numerical results indicate that the linear and nonlinear parts of the absorption coefficients related with intersubband 1 s → 1 p and 1 p → 1 d donor transitions undergo significant changes. [ABSTRACT FROM AUTHOR]

This article presents a theoretical study of the electronic, impurity-related, and nonlinear optical properties of CdS/ZnS quantum dots subjected to electric and magnetic fields. The magnetic field is applied along the z-axis, with the donor impurity always located in the center of the quantum dot. In the case of the electric field, two situations have been considered: applied along the z-axis and applied in the radial direction (central electric field). In both cases, the azimuthal symmetry (around the z-axis) is preserved. In the absence of a magnetic field and considering a central electric field, the system preserves its spherical symmetry both in the presence and in the absence of the donor impurity. The study is carried out in the effective mass approximation and it uses the finite element method to find the eigenfunctions and their corresponding energies, both in the presence and in the absence of the impurity. This work investigates the optical absorption coefficient and the relative change of the refractive index, considering only intraband transitions between l = 0 states (states with azimuthal symmetry concerning the z-axis). Calculations are for z-polarized incident radiation. The study shows that the combined effects of a central electric field and a z-directed magnetic field can give rise to a typical core/shell-like quantum confinement with oscillations of the electron ground state. Additionally, it is shown that the presence of the donor impurity suppresses such oscillations and it is responsible for blue shifts in the optical properties and magnifications of the corresponding resonances.

In this study, self-polarization (SP) for the first excited state in the finite quantum well is presented by taking into account the hydrostatic pressure and the external electric field. We calculated the SP of the first excited state by using the variational method under the effective mass approximation. These calculations were made for different values of the quantum well-width, hydrostatic pressure, external electric field and impurity positions. Our results indicate that the self-polarization of the first excited state in finite quantum well depends remarkably on the hydrostatic pressure, external electric field strength and impurity position. [ABSTRACT FROM AUTHOR]

We investigated comparatively the electronic and optical properties of GaAs/GaAlAs pseudo-elliptic quantum rings with donor impurity under magnetic field in the absence and the presence of electron spin, taken into account through Rashba and Dresselhaus spin–orbit couplings and Zeeman effect. The energy and absorption spectra were computed for four representative positions of the donor impurity (edges and x(y)-middle of the ring). Both approaches demonstrate the important role played by the impurity position, with the strongest effects corresponding to the impurity placed in the middle of the ring. In the spin absence, the impurity position influences both the energies of the absorption peaks and their oscillatory behaviours in energy and amplitude. In the presence of electron spin, the absorption spectra of the pseudo-elliptic quantum ring become more complex at large magnetic fields as the number of transitions is increased by the splitting of the energy levels and present new distinct features at low and high energies that could be observed experimentally. [ABSTRACT FROM AUTHOR]

Using the variational method within the effective-mass approximation, the effects of geometrical shape and impurity position on the ground-state self-polarization and binding energy of a donor impurity are theoretically studied for the infinite GaAs/AlAs tetragonal quantum dot. We have found that the ground-state self-polarization and binding energy depend on geometrical shape and impurity-AlAs layer distance. [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]

The dependence of the magnetization and magnetic susceptibility of donor impurity in parabolic GaAs (Gallium Arsenide) quantum dot has been investigated, at finite temperature under the influence of external tilted electric and magnetic fields. Based on the effective mass approximation, the Hamiltonian of an electron confined in a parabolic quantum dot in the presence of donor impurity which is presented in electric and magnetic fields has been solved by employing the numerical diagonalization method of the Hamiltonian matrix. All the energy matrix elements have been obtained in analytical form. We have shown the variations of the statistical energy and binding energy of donor impurity with the electric and magnetic field strengths and tilt electric field angle. The computed results show that the electrical field can tune the magnetic properties of the QD GaAs medium by flipping the sign of its magnetic susceptibility from diamagnetic (χ 0).

The properties of the conduction band energy states of an electron interacting with a donor impurity center in spherical sector-shaped GaAs-Al0.3Ga0.7As quantum dots are theoretically investigated. The study is performed within the framework of the effective mass approximation through the numerical solution of the 3D Schrödinger equation for the envelope function via the finite element method. The modifications undergone by the spectrum due to the changes in the conical structure geometry (radius and apical angle) as well as in the position of the donor atom are discussed. With the information regarding electron states the linear optical absorption coefficient associated with transition between confined energy levels is evaluated and its features are discussed. The comparison of results obtained within the considered model with available experimental data in GaAs truncated-whisker-like quantum dots shows very good agreement. Besides, our simulation leads to identify the lowest energy photoluminescence peak as donor-related, instead of being associated to acceptor atoms, as claimed after experimental measurement (Hiruma et al. (1995) [14]). Also, a checking of our numerical approach is performed by comparing with analytical solutions to the problem of a spherical cone-shaped GaN with infinite confinement and donor impurity located at the cone apex. Coincidence is found to be remarkable.

Nanoflakes ultra-thin quantum dots are theoretically studied as innovative nanomaterials delivering outstanding results in various high fields. In this work, we investigated the surface properties of an electron confined in spherical ultra-thin quantum dots in the presence of an on-center or off-center donor impurity. Thus, we have developed a novel model that leads us to investigate the different nanoflake geometries by changing the spherical nanoflake coordinates (R, α, ϕ). Under the infinite confinement potential model, the study of these nanostructures is performed within the effective mass and parabolic band approximations. The resolution of the Schrödinger equation is accomplished by the finite difference method, which allows obtaining the eigenvalues and wave functions for an electron confined in the nanoflakes surface. Through the donor and electron energies, the transport, optoelectronic, and surface properties of the nanostructures were fully discussed according to their practical significance. Our findings demonstrated that these energies are more significant in the small nanoflakes area by altering the radius and the polar and azimuthal angles. The important finding shows that the ground state binding energy depends strongly on the geometry of the nanoflakes, despite having the same surface. Another interesting result is that the presence of the off-center shallow donor impurity permits controlling the binding energy, which leads to adjusting the immense behavior of the curved surface nanostructures.

The states of a single dopant centre in zinc-blende GaN-based conical quantum dots with spherical cap are theoretically investigated by analytically solving the corresponding effective mass equation taking advantage of the localisation of the ionised impurity at the cone apex. Nonlinear optical response is analysed through the calculation of the coefficients of optical absorption, relative refractive index change, and second and third harmonic generation, for the chosen set of allowed electron-donor states. The behaviour of the calculated optical quantities under changes in the geometry of the system due to variations in apical width and quantum dot radius is analysed and discussed. [ABSTRACT FROM AUTHOR]

In this research paper, we investigate the impact of the confinement nature on a neutral hydrogenic donor impurity (D 0) in a quantum dot (QD). To investigate the system, we employ the exponential power potential in the presence of Rashba and Dresselhaus spin-orbit interactions, and an external magnetic field. Using the variational method, we calculated the ground state and first excited state energies. We obtained the corresponding binding energies, stable temperatures, transition energy, magnetic susceptibilities, and oscillator strength as a function of various QD parameters and potential shapes. Our findings demonstrate intriguing behavior in response to changes in potential shape, quantum dot parameters, and spin-orbit coupling strengths. These findings provide important insights into the fundamental physics of QDs and impurities, and they may help in designing and optimizing QD-based technologies like sensors and detectors. • On-center D 0 impurity in a GaAs power-exponential quantum dot is studied in a magnetic field with spin-orbit interactions. • The ground state and excited state energies are obtained by a variational method. • By equating the maximum binding energy to k B T , we calculate the stable temperatures of both the states of the D 0 impurity system. • The susceptibility, transition energy, and oscillatory strength (OS) are also determined. • OS depends significantly on the steepness parameter (q) in the presence of both SOIs. [ABSTRACT FROM AUTHOR]

• Off-center D 0 impurity in a Gaussian GaAs quantum dot is studied in a magnetic field with spin–orbit interactions. • The ground state and first excited state energies are obtained by a variational method. • Equating the maximum binding energy to k B T , we calculate the stable temperatures of both the states of the D 0 impurity.. • The susceptibility, transition energy, and oscillatory strength are also determined. • Electronic, magnetic, and optical properties depend on the strength of the dot V 0 , B and spin–orbit interactions. The Rashba and Dresselhaus spin–orbit interactions (SOIs) and the magnetic field effects on off-center hydrogen donor impurity D 0 in a two-dimensional Gaussian GaAs quantum dot (QD) are investigated. By performing a unitary transformation, the effect of the SOI incorporated and retained terms up to quadratic in the SOI constants (λ R , λ D). The variational method is engaged for the ensuing Hamiltonian with improved wave functions to determine the ground, first exited state energies, binding energies, transition energy and susceptibility of a (D 0) impurity. The results show that the Rashba spin–orbit interaction (RSOI) reduces, the Dresselhaus spin–orbit interaction (DSOI) and magnetic field enhances the energy of the (D 0) impurity. By equating the maximum binding energy of the D 0 system with K B T , we calculated the temperatures of the stable D 0 impurity. Finally, we calculated the oscillator strength (OS) and compared it to the available literature. OS shows remarkable behaviour to SOIs and QD parameters. [ABSTRACT FROM AUTHOR]

We present a theoretical study to investigate the effect of donor impurity on the magnetization (M) and the magnetic susceptibility (χ) of single electron quantum dot (QD) with Gaussian confinement in the presence of a magnetic field. We solve the Hamiltonian of this system, including the spin, by using the exact diagonalization method. The ground state binding energy (BE) of an electron has been shown as a function of QD radius and confinement potential depth. The behaviors of the magnetization and the magnetic susceptibility of a QD have been studied as a function of temperature, confinement potential depth, quantum radius and magnetic field. We have shown the effect of donor impurity on the magnetization and magnetic susceptibility curves of Gaussian quantum dot (GQD). [ABSTRACT FROM AUTHOR]

• Spin-orbit interaction effect on a D 0 centre is studied in a quantum dot in a magnetic field. • Binding energy, magnetization and susceptibility are obtained by a variational method. • Magnetization and Susceptibility are found to be diamagnetic in nature. • Rashba interaction is found to reduce the binding energy and enhance the diamagnetic susceptibility. • Dresselhaus interaction enhances the binding energy but decreases the diamagnetic susceptibility. The binding energy of a hydrogenic-like donor complex D 0 placed in a two-dimensional Gaussian quantum dot GaAs semiconductor is determined incorporating the Rashba and Dresselhaus spin-orbit interactions in the presence of an externally applied magnetic field. A unitary transformation is employed to deal with the spin-orbit interactions and their effects are incorporated up to second order in the coupling coefficients. The resulting Hamiltonian is solved variationally using a simple wave function. The results indicate that the Rashba spin-orbit interaction and the confining potential reduce the energy of the donor complex whereas the magnetic field enhances it. Interestingly enough, the binding energy is enhanced by the Dresselhaus spin-orbital interaction in the presence of a magnetic field and while it is reduced in the absence of it. Finally we study the effect of magnetic field and spin-orbit interactions on the magnetic moment and susceptibility. [ABSTRACT FROM AUTHOR]

In the present work, the exact diagonalization method had been implemented to calculate the ground state energy of shallow donor impurity located at finite distance along the growth axis in GaAs/AlGaAs heterostructure in the presence of a magnetic field taken to be along z direction. The impurity binding energy of the ground state had been calculated as a function of confining frequency and magnetic field strength. We found that the ground state donor binding energy (BE) calculated at ωc =2R * and * ω = 5.421R , decreases from BE=7.59822 R * to BE=2.85165 R * , as we change the impurity position from d=0.0 a* to d=0.5 a* , respectively .In addition, the combined effects of pressure and temperature on the binding energy, as a function of magnetic field strength and impurity position, had been shown using the effective-mass approximation. The numerical results show that the donor impurity binding energy enhances with increasing the pressure while it decreases as the temperature decreases. [ABSTRACT FROM AUTHOR]

The possibility of determining in-depth distribution of tellurium donor impurity in lamellar bismuth samples using the time-of-flight mass spectrometry and electron microscopy methods in the concentration range of 0.005-0.150 at. % Te is studied in the present paper. To measure the amount of tellurium in lamellar bismuth samples, we used a LUMAS-30 time-of-flight mass spectrometer with a pulsed low-pressure glow gas discharge in a combined hollow cathode and a Zeiss Evo-40 scanning electron microscope. The samples for measurements were cut from the middle of the ingots of the Bi-Te alloy with the required impurity concentration. The samples presented a thin plate of a size of 10 × 10 mm2 and 1 mm thickness. The samples were thoroughly washed in distilled water and then etched in a 65 % solution of nitric acid to remove the surface layer with traces of external contaminants. The samples were strengthened as the bottom of the hollow cathode in the gas-discharge cell, where the impulse ionization of the sample atoms in a glow discharge plasma occurred. The relative error in the in-depth distribution of impurities did not exceed 6 %, while the error in determining the concentration of impurities by a mass spectrometer, according to the passport data, did not exceed 5 %. The sensitivity limit in determining the concentration of impurities in the device LUMAS-30, according to the passport data, was 10 – 6 at. %. As a result of research, we set that the time-of-flight mass spectrometry method gives a very accurate determination of the tellurium impurity concentration, and also allows to establish a uniform distribution of tellurium over the volume of a doped bismuth lamellar sample. The electron microscopy method using a Zeiss Evo-40 microscope does not give a uniform distribution of tellurium over the sample volume [ABSTRACT FROM AUTHOR]

We have theoretically investigated the electronic properties and nonlinear optical rectification spectra of GaAs/AlGaAs anisotropic quantum ring, modelled by an outer ellipsis and an inner circle, in connection to the presence of a donor off-centre impurity, structural distortions and in-plane electric field. The one-electron energy spectrum and wave functions are found using the adiabatic approximation and the finite element method within the effective-mass model. The energy spectrum of concentric ring reveals an anomalous oscillatory behaviour in the region of relatively small values of the electric field (< 12 kV/cm) followed by linear Stark effect at higher field values. We showed that this unusual behaviour is strongly affected by the ratio of the outer/inner ring radii, the displacement of the inner circle (eccentricity) along the x or y axis and the impurity presence. The related nonlinear optical rectification spectra present maxima whose positions mirror this oscillatory behaviour and consequently can be used as an excellent tool to distinguish the presence of an impurity or the direction of the eccentricity. [ABSTRACT FROM AUTHOR]

Abstract We have investigated the binding energies of the s -symmetric ground and first excited shallow donor impurity states and the total 1 s → 2 s absorption coefficient, including the first and third order corrections, in "12-6" tuned GaAs/GaAlAs double quantum well as a function of the impurity position, size of the structure, and the electric and magnetic field intensities. The obtained results show that the electronic and optical properties of tuned GaAs/GaAlAs double quantum well can be adjustable by an appropriate choice of the sample geometry, material parameters and applied external fields which will lead to new potential applications in optoelectronics. Highlights • Donor impurity states in "12-6" tuned double quantum well. • Nonlinear optical absorption related to s-symmetric states. • Electromagnetic field is used to tune the optical absorption. • The impurity binding energy depends on the double well parameter. [ABSTRACT FROM AUTHOR]

The dependence of the magnetization and magnetic susceptibility of donor impurity in parabolic GaAs (Gallium Arsenide) quantum dot has been investigated, at finite temperature under the influence of external tilted electric and magnetic fields. Based on the effective mass approximation, the Hamiltonian of an electron confined in a parabolic quantum dot in the presence of donor impurity which is presented in electric and magnetic fields has been solved by employing the numerical diagonalization method of the Hamiltonian matrix. All the energy matrix elements have been obtained in analytical form. We have shown the variations of the statistical energy and binding energy of donor impurity with the electric and magnetic field strengths and tilt electric field angle. The computed results show that the electrical field can tune the magnetic properties of the QD GaAs medium by flipping the sign of its magnetic susceptibility from diamagnetic (χ < 0) to paramagnetic (χ > 0). [ABSTRACT FROM AUTHOR]

The influence of a constant magnetic field and the position of a shallow donor impurity on the energy spectrum of an electron and its probability density distribution in a spherical AlxGa1-xAs/GaAs/AlxGa1-xAs nanosystem has been studied. In the approximation of the effective mass and the model of rectangular wells and barriers, the solutions of the Schrödinger equation have been obtained by the expansion of the ground and excited state wave functions of an electron on the basis of the exact wave functions in the absence of a magnetic field and an impurity have been found. It has been shown that with increasing magnetic field induction, the role of the electron ground state in the nanosystem without impurities is consistently performed by the states with the magnetic quantum number m = 0, - 1, - 2, ... (the Aharonov-Bohm effect). It has been established that the period of such oscillations of the electron ground state does not depend on the potential barriers height. However, the presence of an off-central donor impurity located in a potential well of the nanosystem, results in the vanishing of the Aharonov-Bohm effect. The dependences of the electron energy spectrum and wave functions on the position of an impurity shifted from the nanosystem center along and perpendicular to the magnetic field direction have been obtained. It has been shown that in the first case, the quantum states are characterized by a certain value of the magnetic quantum number m, and the expansion contains only wave functions of states with this value of m. In the second case, the problem loses cylindrical symmetry and new quantum states are formed from the states with different values of all three quantum numbers n, l, m. [ABSTRACT FROM AUTHOR]

The theoretical study of the energy spectrum and optical response of off-axis donor in a GaAs quantum ribbon with anisotropic rim height under the presence of constant crossed electric and magnetic fields is presented. The calculations are carried out within the effective mass and parabolic approximation, using an adiabatic approach combined with a diagonalization scheme. The rim height of the quantum ribbon has been modeled by including a phenomenological two-parametric function that accounts for realistic features of multi-hilled semiconductor nanostructure obtained from atomic force microscopy images. The first phenomenological parameter is introduced to control the number of quantum ribbon structural hills and the second one to deal with the height of the hills. It is shown that both the depth and the number of structural hills tend to substantially affect the Aharonov–Bohm oscillation pattern which can be quenched or restored by applying an electric field in an appropriate direction. The effect of the changes in the geometry and in the applied electric field onto the optical absorption and refractive index change are discussed. The phenomenon of electric-field-induced optical transparency in the system is particularly highlighted. [ABSTRACT FROM AUTHOR]

This work reports on theoretical investigation of the temperature and hydrostatic pressure effects on the confined donor impurity in a AlGaAs-GaAs hollow cylindrical core-shell quantum dot. The charges are assumed to be completely confined to the interior of the shell with approximately rigid walls. Within the framework of the effective-mass approximation and by using a variational approach, we have computed the donor binding energies as a function of the shell size in order to study the behavior of the electron-impurity attraction for a very small thickness under the influence of both temperature and hydrostatic pressure. Our results show that the temperature and hydrostatic pressure have a significant influence on the impurity binding energy for large shell quantum dots. It will be shown that the binding energy is more pronounced with increasing pressure and decreasing temperature for any impurity position and quantum dot size. The photoionization cross section is also analyzed by considering only the in-plane incident radiation polarization. Its behavior is investigated as a function of photon energy for different values of pressure and temperature. The opposite effects caused by temperature and hydrostatic pressure reveal a big practical interest and offer an alternative way to tuning of correlated electron-impurity transitions in optoelectronic devices. [ABSTRACT FROM AUTHOR]

The electron states in a holey elliptically shaped GaAs quantum dot are investigated within the effective mass scheme with the use of the adiabatic approximation and the finite element method. The effects of a donor impurity center and an applied electric field are particularly taken into account. Electron‐impurity energies are reported as functions of both the geometry of the quantum dot and the applied field intensity, whereas temperature effects are also included. The analysis of electron‐impurity intersubband transitions allows the investigation of the light absorption response of the system. [ABSTRACT FROM AUTHOR]

The effect of homogeneous magnetic field and location of donor impurity on the electron energy spectrum and distribution of its probability density in spherical core-shell quantum dot is investigated. In the framework of the effective mass approximation and rectangular infinitely deep potential well, the solutions of the Schrodinger equation are found using the matrix method. The wave functions are expanded over the complete set of exact functions obtained without the magnetic field and impurity. It is shown that when the induction of magnetic field increases, the ground state of electron in the nanostructure without impurity or on-center impurity is successively formed by the states with m = 0, −1, −2, … (Aharonov-Bohm effect). When donor impurity is located in the shell of the nanostructure the Aharonov-Bohm effect vanishes. The dependences of electron energy spectrum and its wave functions on the location of impurity, placed along the direction of magnetic field or perpendicularly to it, are studied. It is shown, that in the first case, the quantum states are characterized by the certain value of magnetic quantum number m and the expansion contains the wave functions of the states with it only. In the second case, the cylindrical symmetry of the problem is broken and the new quantum states are formed from the states with different values of all three quantum numbers n , l , m and electron energy spectrum weakly depends on the magnetic field induction. [ABSTRACT FROM AUTHOR]

Theoretical investigations are carried out of binding energies of a donor charge assumed to be located exactly at the center of symmetry of two concentric cylindrical quantum wires. The intrinsic confinement potential in the region of the inner cylinder is modeled in any one of the three profiles: simple parabolic, shifted parabolic or the polynomial potential. The potential inside the shell is taken to be a potential step or potential barrier of a finite height. Additional confinement of the charge carriers is due to the vector potential of the axial applied magnetic field. It is found that the binding energies attain maxima in their variations with the radius of the inner cylinder irrespective of the particular intrinsic confinement of the inner cylinder. As the radius of the inner cylinder is increased further, the binding energies corresponding to either the parabolic or the polynomial potentials attain minima at some critical core-radius. Finally, as anticipated, the binding energies increase with the increase of the parallel applied magnetic field. This behaviour of the binding energies is irrespective of the particular electric potential of the nanostructure or its specific dimensions. [ABSTRACT FROM AUTHOR]

In this paper we present a theoretical investigation of quantum confinement effects on the electron and single donor states in G a N conical quantum dot with spherical edge. In the framework of the effective mass approximation, the Schrödinger equations of electron and donor have been solved analytically in an infinite potential barrier model. Our calculations show that the energies of electron and donor impurity are affected by the two characteristic parameters of the structure which are the angle Ω and the radial dimension R . We show that, despite the fact that the reduction of the two parameters Ω and R leads to the same confinement effects, the energy remains very sensitive to the variation of the radial part than the variation of the angular part. The analysis of the photoionization cross-section corresponding to optical transitions between the conduction band and the first donor energy level shows clearly that the reduction of the radius R causes a shift in resonance peaks towards the high energies. On the other hand, the optical transitions between 1 s − 1 p , 1 p − 1 d and 1 p − 2 s show that the increment of the conical aperture Ω (or reduction of R ) implies a displacement of the excitation energy to higher energies. [ABSTRACT FROM AUTHOR]

The second-order nonlinear optical susceptibility in a cylindrical quantum dot (CQD) of G a A s / G a 0.6 A l 0.4 A s with a donor impurity inside under the influence of a uniform magnetic field applied in the axial direction of the cylinder is studied theoretically. Using the variational method, the energies and the wave functions of the 1 S − l i k e , 2 P − − l i k e , and 2 P + − l i k e impurity states were found when it moves inside of the CQD. It was found that there is a degeneration of the energy of the impurity for the 2 P − − l i k e and 2 P + − l i k e states in the absence of magnetic field, producing two resonant peaks for the second-harmonic generation (SHG) for any position of the impurity. This degeneration is split only when a magnetic field is applied, indicating a Zeeman effect in the system. Thus the variation of the intensity of the magnetic field allows tuning the condition of resonance of two photons. It was also found that the increase in the radial position of the impurity produces an increase in the intensity of the peaks of the optical rectification (OR) and SHG coefficients, therefore a variation of the position of the impurity in a CQD allows modulating the intensity of the second-order nonlinear optical response. [ABSTRACT FROM AUTHOR]

We study the effect of Γ-X band crossover due to the application of hydrostatic pressure of a hydrogenic donor confined in a Triangular GaAs/Al 1-x Ga x As Quantum Well (TQW) for x = 0.3 and the diamagnetic susceptibility (χ dia ) for such an impurity in 1s and some few low lying excited states have been investigated. The Schrodinger equation has been solved using variational technique in the effective mass approximation. The results show that the diamagnetic susceptibility (χ dia ) of a hydrogenic donor abruptly increases at a particular pressure for 1s and 2p ± states but a steady increase for 2s state as a function of applied pressure. [ABSTRACT FROM AUTHOR]

An investigation of the nonlinear optical rectification of a GaAs two-dimensional disc-shaped quantum ring with an off-center donor impurity under magnetic field has been performed by using a variational method in the effective mass approximation. The two-dimensional quantum ring was described by a pseudo-harmonic potential. The results are presented as functions of the incident photon energy for the different values of the impurity position and the magnetic field. It is found that the nonlinear optical rectification spectra are strongly affected by the position of the off-center impurity and the magnetic field. [ABSTRACT FROM AUTHOR]

A spherical quantum dot (QD) heterosystem CdS/SiO2 has been studied. Each QD has a hydrogen-like impurity in its center. Besides that, it has been accounted that a polarization trap for electron exists at the interfaces due to the difference between the QD and matrix dielectric permittivity. It has been defined that for small QD radii there are surface electron states. For different radii, partial contributions of the surface states into the electron energy caused by the electron-ion and electron-polarization charges interaction have been defined. The linear light absorption coefficient of noninteracting QDs has been calculated taking into account the QD dispersion by the size. It is shown that the surface states can be observed into different ranges of an electromagnetic spectrum. [ABSTRACT FROM AUTHOR]