Binding Energy Of Shallow Donors Research Articles

Binding energies of shallow donors in polar ZnO/ZnBeO quantum well

This study examines a single wurtzite ZnO/ZnBeO quantum well structure oriented in the polar c-direction. The focus is on investigating the binding energies associated with an impurity donor atom within this system. To achieve this, a self-consistent solution to the Schrödinger and Poisson equations is obtained using the finite difference method. The framework employed involves the effective mass and envelope function approximations. The impurity is represented using a hydrogenic-type wave function, and donor binding energies are determined via a variational approach. The research analyzes the binding energies of the 1s and 2p± states, along with the transition energy between them. These quantities are explored as functions of the well width and Be concentration, considering donor positions at the right and left interfaces as well as at the well’s center. Furthermore, the impact of an external magnetic field oriented along the growth direction is assessed, spanning up to 10T, in order to quantify changes in the binding energies. The presence of a built-in electric field induces an asymmetric band profile and a triangular well configuration. This asymmetry results in a loss of symmetry within the binding energy curves. Ultimately, the investigation culminates in the computation of the oscillator strength governing transitions between the donor states. When the donor is situated at the right interface, the energy values remain relatively constant as the well width increases, and the oscillator strength values demonstrate a consistent linear rise.

Effect of electric field on the binding energy and polarisation of shallow donor in a GaAs/Ga1-xAlxAs pillbox surrounded by Ga1-yAlyAs

ABSTRACT 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.

Ground-state Shallow-donor Binding Energy in (In,Ga)N/GaN Double QWs Under Temperature, Size, and the Impurity Position Effects

In this paper, we study the hydrogen-like donor-impurity binding energy of the ground-state change as a function of the well width under the effect of temperature, size, and impurity position. Within the framework of the effective mass approximation, the Schrodinger-Poisson equation has been solved taken account an on-center hydrogen-like impurity in double QWs with rectangular finite confinement potential profile for 10% of indium concentration in the (well region). The eigenvalues and their correspondent eigenvectors have been obtained by the fined element method (FEM). The obtained results are in good agreement with the literature and show that the temperature, size, and the impurity position have a significant impact on the binding energy of a hydrogen-like impurity in symmetric double coupled quantum wells based on non-polar wurtzite (In,Ga) N/GaN core/Shell.

Role of a uniform magnetic field on the energy spectrum of a single donor in a core/shell spherical quantum dot

Using the variational approach within the framework of the effective-mass approximation (EMA), the binding energy of a centred hydrogenic donor impurity in a CdSe/ZnTe core/shell spherical quantum dot (CSSQD) in the presence of an external magnetic field was investigated. In this model, we have taken into account the effect of the radial dependence of the dielectric constant and of the electron effective mass. Our numerical results show a remarkable influence of the nanodot spatial parameters and of the external magnetic field strength on the shallow donor binding energy.

Electric field effect on lowest excited-state binding energy of hydrogenic impurity in (In,Ga)N parabolic wire

Externally applied electric field and effective radius effects are investigated on the lowest excitedstate shallow-donor binding energy in (In,Ga)N-GaN parabolic wire within the framework of single band effective-mass approximation. The calculations are performed using the finite-difference method within the quasi-one-dimensional effective potential model. Our results reveal that: (i) the probability density is the largest on a circularity whose radius is the effective radius, (ii) the lowest excited-state binding energy is the largest for impurity located on this circularity while it starts to decrease when the impurity is away from the circularity and (iii) the binding energy is strongly-dependent on the complex interplay of spatial confinement, coulomb interaction and applied electric field.

Energy Spectra of CdS/Cd1-xZnx S Nano Dot Under The Influence of Magnetic Field

We present a theoretical study on shallow donor binding energies of CdS/ CdZnS nano dot as a strength of applied magnetic field along Z direction for various Zn concentration. Calculations are carried out by using the technique of variational ansatz within the frame work of effective mass approximation. Our results show that the binding energies are drastically affected by the dot radius, the strength of magnetic field and concentrations.

Magnetic field-dependent of binding energy in GaN/InGaN/GaN spherical QDQW nanoparticles

Simultaneous study of magnetic field and impurity's position effects on the ground-state shallow-donor binding energy in GaN│InGaN│GaN (core│well│shell) spherical quantum dot–quantum well (SQDQW) as a function of the ratio of the inner and the outer radius is reported. The calculations are investigated within the framework of the effective-mass approximation and an infinite deep potential describing the quantum confinement effect. A Ritz variational approach is used taking into account of the electron-impurity correlation and the magnetic field effect in the trial wave-function. It appears that the binding energy depends strongly on the external magnetic field, the impurity's position and the structure radius. It has been found that: (i) the magnetic field effect is more marked in large layer than in thin layer and (ii) it is more pronounced in the spherical layer center than in its extremities.

Theoretical investigation of stark effect on shallow donor binding energy in InGaN spherical QD-QW

In this paper, a simultaneous study of electric field and impurity's position effects on the ground-state shallow-donor binding energy in GaN│InGaN│GaN spherical quantum dot-quantum well (SQD-QW) as a function of the ratio of the inner and the outer radius is reported. The calculations are investigated using variational approach within the framework of the effective-mass approximation. The numerical results show that: (i) the binding energy is strongly affected by the external electric field and the SQD-QW dimension, (ii) a critical value of spherical system's radius is obtained constituting the limit of three dimension confinement and spherical thin layer confinement and (iii) the Stark shift increases with increasing electric field and it is more pronounced around the position of the impurity corresponding to the binding energy maxima than in the spherical layer extremities.

Magneto-donors in laser-dressed inverse parabolic quantum wells

By using a nonperturbative theory within the effective mass approximation, the combined effects of the intense laser radiation and applied magnetic field on the shallow-donor binding energy in inverse parabolic quantum wells are investigated. It is found that: (i) the increasing of the laser intensity dramatically modifies the confinement potential shape leading to the formation of a multiple well potential within the structure; (ii) the binding energy as a function of the impurity position and external fields follows a similar behavior to that observed for the spatial distribution of the electron wave function; (iii) the peak positions in valence-to-donor-related absorption spectra can be tuned at specific energies by changing the external field strengths. Our results suggest that this profile could be used in designing new devices with properties controlled by laser and magnetic fields.

Simultaneous effects of dielectric mismatch and electric field on the electronic properties in Si nanodots

By using the finite element method within the effective mass approximation, the effects of both dielectric confinement and electric field on the shallow-donor binding energy and polarizability in spherical Si quantum dots are investigated. It is found that: (i) the ground state binding energy is significantly increased by the dielectric mismatch at the dot interface, (ii) in the freestanding nanodot the competition between the electric field, polarization charges induced at interfaces and impurity position determines the symmetry of the electron probability distribution; (iii) the donor polarizability decreases with electric field strength and this effect is more pronounced for large dielectric mismatches. Therefore, the electronic properties of the nanocrystals could be tuned by proper tailoring of the surrounding medium dielectric constant as well as by varying the electric field. The normalized binding energy of an on-center hydrogenic donor is also been estimated and the results are in good agreement with the previous reported values.

Photoluminescence study of aligned ZnO nanorods grown using chemical bath deposition

The photoluminescence study of self-assembled ZnO nanorods grown on a pre-treated Si substrate by a simple chemical bath deposition method at a temperature of 80°C is hereby reported. By annealing in O2 environment the UV emission is enhanced with diminishing deep level emission suggesting that most of the deep level emission is due to oxygen vacancies. The photoluminescence was investigated from 10K to room temperature. The low temperature photoluminescence spectrum is dominated by donor-bound exciton. The activation energy and binding energy of shallow donors giving rise to bound exciton emission were calculated to be around 13.2meV, 46meV, respectively. Depending on these energy values and nature of growth environment, hydrogen is suggested to be the possible contaminating element acting as a donor.

The high hydrostatic pressure effect on shallow donor binding energies in GaAs–(Ga, Al)As cylindrical quantum well wires at selected temperatures

We have presented the behavior of a shallow donor impurity with binding energy in cylindrical-shaped GaAs/Ga 0.7Al 0.3As quantum well wires under high hydrostatic pressure values. Our results are obtained in the effective mass approximation using the variational procedures. In our calculations, we have not considered the pressure related Γ−X crossover effects. The hydrostatic pressure dependence on the expectation value of ground state binding energy is calculated as a function of wire radius at selected temperatures. We have also discussed the effects of high hydrostatic pressure and temperature on some physical parameters such as effective mass, dielectric constant, and barrier height. A detailed analysis of these calculations has proved that the effective mass is the most important parameter, which explains the dependency of donor impurity binding energies on the high hydrostatic pressure values.

DONOR AND ACCEPTOR STATES IN GaAs-(Ga, Al)As QUANTUM DOTS: EFFECTS OF HYDROSTATIC PRESSURE AND AN INTENSE LASER

We calculated the binding energies of shallow donors and acceptors in a spherical GaAs - Ga 1-x Al x As quantum dot under the combined effect of isotropic hydrostatic pressure and an intense laser. We used a variational approach within the effective mass approximation. The binding energy was computed as a function of hydrostatic pressure, dot sizes and laser field amplitude. The results showed that the impurity binding energy increases with pressure and decreases with the laser field amplitude when other parameters are fixed. We also found that the pressure effects are more dramatic for donor than acceptor impurities, especially for quantum dots with small radii.

An analysis of the effect of nitrogen and a screened (by free carriers) Coulomb field on the binding energy of hydrogenic shallow donors in GaInAsN

The effect of nitrogen concentration on the screening with free carriers and binding energy of hydrogenic shallow donors in GaInAsN alloys is investigated. The binding energy is calculated using a novel algebraic model which was proposed recently by Gönül et al. (2006) [16], in order to find an analytical solution to the screened Coulomb potential. The results show that the nitrogen concentration is a strong factor in producing a screening field of free carriers and in affecting the binding energy of hydrogenic shallow donors.

Binding energy of an off-center shallow donor [formula omitted] in a spherical quantum dot

The binding energy of a negatively charged hydrogenic impurity with on- and off-center positions in a spherical Gaussian quantum dot was calculated with the configuration interaction method. Our calculations show that E b is always positive for on-center impurities with a maximum near to the radius for one-electron stability of the potential well R c . For off-center positions the binding energy can assume negative values within a range of the quantum dot radius, thus indicating the instability of the system.

Shallow impurity absorption spectroscopy in isotopically enriched silicon

Inhomogeneous broadening due to isotopic randomness in natural Si has been shown to cause a broadening of many of the ground-state to excited-state infrared-absorption transitions of the shallow donor phosphorus and acceptor boron. Previously, it had been thought that the observed linewidths of shallow impurity transitions in silicon were at their fundamental lifetime limit. We report improved high-resolution infrared-absorption studies of these transitions in new samples of isotopically enriched $^{28}\text{S}\text{i}$, $^{29}\text{S}\text{i}$, and $^{30}\text{S}\text{i}$. Some of the transitions in $^{28}\text{S}\text{i}$ show the narrowest linewidths ever reported for shallow donor and acceptor absorption transitions, and many higher excited states are now observed. The improved samples of $^{29}\text{S}\text{i}$ and $^{30}\text{S}\text{i}$ result in revised values for the dependence of shallow donor and acceptor binding energies on the average Si mass.

Donor binding energy and thermally activated persistent photoconductivity in high mobility (001) AlAs quantum wells

A doping series of AlAs (001) quantum wells with Si δ-modulation doping on both sides reveals different dark and postillumination saturation densities, as well as temperature dependent photoconductivity. The lower dark two-dimensional electron density saturation is explained assuming deep binding energy of ΔDK=65.2meV for Si donors in the dark. Persistent photoconductivity (PPC) is observed upon illumination, with higher saturation density indicating shallow postillumination donor binding energy. The photoconductivity is thermally activated, with 4K illumination requiring postillumination annealing to T=30K to saturate the PPC. Dark and postillumination doping efficiencies are reported.

Impurity states in a spherical GaAs–Ga[formula omitted] Al[formula omitted]As quantum dots: Effects of hydrostatic pressure

We calculated the binding energies of shallow donors and acceptors in a spherical GaAs–Ga1-xAlxAs quantum dot under isotropic hydrostatic pressure for both a finite and an infinitely high barrier. We use a variational approach within the effective mass approximation. The binding energy is computed as a function of hydrostatic pressure, the dot sizes and the impurity position. The results show that the impurity binding energy increases with the pressure for any position of the impurity. We have also found that the binding energy depends on the location of the impurity and the pressure effects are less pronounced for impurities on the edge.

Binding energy of shallow donors in a quantum well in the presence of a tilted magnetic field

We present results of variational calculations of the binding energy of a neutral donor in a quantum well in the presence of a magnetic field tilted relative to the QW plane. Assuming that the donor is located in the center of the QW, we perform calculations for parameters typical of a II-VI wide-gap semiconductor heterostructure, using as an example the case of a rectangular CdTe quantum well with CdMgTe barriers. We present the dependence of the binding energy of a neutral donor on the tilt angle and on the magnitude of the applied magnetic filed. As a key result, we show that measurement of the binding energy of a donor at two angles of the magnetic field with respect to the quantum well plane can be used to unambiguously determined the conduction band offset of the materials building up heterostructure.

Hydrostatic pressure effects on donor-related absorption spectra in GaAs–Ga 1−xAl xAs quantum wells

In this paper, the effects of hydrostatic stress on the density of donor impurity states and donor-related optical absorption spectra in a GaAs–Ga 1− x Al x As quantum wells are obtained. We calculate the shallow-donor binding energy for different well widths and different values of hydrostatic stress. We find that for large well widths the binding energy increases slowly with hydrostatic stress, as opposed to the behavior of the binding energy for wells with small width. One of the results shows that the binding energy does not change appreciably with the impurity position when the width of the well is small and the hydrostatic stress is high. Two structures in both, the density of states and the optical absorption spectra, associated with impurities located close to the center and to the edges of the structure, are obtained. We have also observed that the density of states and the optical absorption spectra depend strongly on the applied hydrostatic stress.