Binding Energy Of Impurity States Research Articles

Diamagnetic Susceptibility and Donor Binding Energy of Impurity States in Zinc Blende AlGaN/GaN Quantum Dot

In the frame work of effective mass approximation, we have determined the donor binding energies of the most minimal donor states, \(1s\), \(2p_0\) and \(2p_{\pm}\), in zinc blende AlGaN/GaN Quantum dot in the impact of the magnetic field along the development(growth) directions. The calculations are performed utilizing variational method. The calculations are performed using variational method. As a function of the quantum dot radius and the applied magnetic field, the donor binding energies and diamagnetic susceptibilities are obtained. The oscillator quality of the potential transitions between the donor states is then figured by displaying them as the conditions of a two-level atom. Our outcomes demonstrate that (i) the donor binding energy is appreciable for smaller dot radii and magnetic field effect is predominant for larger dot radii, (ii) the diamagnetic susceptibility increases with applied magnetic field and is appreciable only for larger dot radii, (iii) The oscillator quality of the potential transitions between the donor states is not pronounced for smaller dot size radii and plays a significant role in larger dot radii.

Impurity Binding Energyin Quantum Dots with Parabolic Confinement in the Presence of Electric Field

We present an efficient method for calculation of the impurity binding energy in a quantum dot with parabolic confinement in the presence of the electric field. The unknown wave function is expanded into a basis of one-dimensional harmonic oscillator states describing the electron's movement perpendicular to the plane of quantum well. Green's function technique used to calculate the coefficients of the expansion. Binding energy of impurity states is defined as poles of the wave function. Developed method applied to calculation of impurity binding energy for different position of impurity and the intensity of electric field.

Impurity binding energies in quantum dots with parabolic confinement

We present an effective numerical procedure to calculate the binding energies and wave functions of the hydrogen-like impurity states in a quantum dot (QD) with parabolic confinement. The unknown wave function was expressed as an expansion over one-dimensional harmonic oscillator states, which describes the electron's movement along the defined z-axis. Green's function technique used to obtain the solution of Schredinger equation for electronic states in a transverse plane. Binding energy of impurity states is defined as poles of the wave function. The dependences of the binding energy on the position of an impurity, the size of the QD and the magnetic field strength are presented and discussed.

Binding energies of impurity states in strained wurtzite GaN/AlxGa1−xN heterojunctions with finitely thick potential barriers

Ground state binding energies of donor impurities in a strained wurtzite GaN/AlxGa1−xN heterojunction with a potential barrier of finite thickness are investigated using a variational approach combined with a numerical computation. The built-in electric field due to the spontaneous and piezoelectric polarization, the strain modification due to the lattice mismatch near the interfaces, and the effects of ternary mixed crystals are all taken into account. It is found that the binding energies by using numerical wave functions are obviously greater than those by using variational wave functions when impurities are located in the channel near the interface of a heterojunction. Nevertheless, the binding energies using the former functions are obviously less than using the later functions when impurities are located in the channel far from an interface. The difference between our numerical method and the previous variational method is huge, showing that the former should be adopted in further work for the relevant problems. The binding energies each as a function of hydrostatic pressure are also calculated. But the change is unobvious in comparison with that obtained by the variational method.

Effects of hydrostatic pressure and external electric field on the impurity binding energy in strained GaN/Al x Ga1−x N spherical quantum dots

The binding energy and Stark effect energy shifts of a shallow donor impurity state in a strained GaN/AlxGa1−xN spherical finite-potential quantum dot (QD) are calculated using a variational method based on the effective mass approximation. The binding energy is computed as a function of dot size and hydrostatic pressure. The numerical results show that the binding energy of the impurity state increases, attains a maximum value, and then decreases as the QD radius increases for any electric field. Moreover, the binding energy increases with the pressure for any size of dot. The Stark shift of the impurity energy for large dot size is much larger than that for the small dot size, and it is enhanced by the increase of electric field. We compare the binding energy of impurity state with and without strain effects, and the results show that the strain effects enhance the impurity binding energy considerably, especially for the small QD size. We also take the dielectric mismatch into account in our work.

Magnetic-Field Effects on Donor Impurity States in a Quantum Well

Green’s function technique is used to obtain the solution of Shredinger equation for impurity states in a quantum well (QW) under the magnetic field. Binding energy of impurity states is defined as poles of the wave function. We studied effects of the magnetic field magnitude and impurity position on the binding energy. The calculations were performed for both ground and excited states. The dependences of binding energies versus impurity position and magnetic field are presented for GaAs/Al0.3Ga0.7As QW.

Screening influence on the Stark effect of impurity states in strained wurtzite GaN/AlxGa1−xN heterojunctions under pressure

The screening effect of the random-phase-approximation on the states of shallow donor impurities in free strained wurtzite GaN/AlxGa1–xN heterojunctions under hydrostatic pressure and an external electric field is investigated by using a variational method and a simplified coherent potential approximation. The variations of Stark energy shift with electric field, impurity position, Al component and areal electron density are discussed. Our results show that the screening dramatically reduces both the blue and red shifts as well as the binding energies of impurity states. For a given impurity position, the change in binding energy is more sensitive to the increase in hydrostatic pressure in the presence of the screening effect than that in the absence of the screening effect. The weakening of the blue and red shifts, induced by the screening effect, strengthens gradually with the increase of electric field. Furthermore, the screening effect weakens the mixture crystal effect, thereby influencing the Stark effect. The screening effect strengthens the influence of energy band bending on binding energy due to the areal electron density.

Stark effects on bound polarons in polar cylindrical quantum wires with finite confining potential

The electric field effects on bound polarons in polar quantum wires with a finite confining potential are studied by a variational method. Both the confined bulk longitudinal optical phonons and the interface optical phonons are taken into account in considering the electron-phonon as well as the impurity-ion phonon couplings. The binding energies are calculated as functions of the transverse dimension of the quantum wire, and the donor-impurity position for different electric fields. The numerical results for the GaAs quantum wire are given and discussed as an example. A peak of the binding energy is found at a certain radius and shift toward a larger radius with applying an electric field. The calculated results confirm that the electron-phonon interaction reduces both the binding energies of impurity states and the Stark shifts and cannot be neglected.

Phonon effect on binding energies of impurity states in cylindrical quantum wires of polar semiconductors under an electric field

Phonon effect on hydrogenic impurity states in cylindrical quantum wires of polar semiconductors under an applied electric field is studied theoretically by a variational approach. The binding energies are calculated as functions of the transverse dimension of the quantum wire, and the donor-impurity position under different fields. The electron–phonon interaction is considered in the calculations by taking both the confined bulk longitudinal optical phonons and interface optical phonons as well as the impurity-ion–phonon coupling. The numerical results for the CdTe and GaAs quantum wires are given and discussed as examples. It is confirmed that the electron–phonon interaction obviously reduces both the binding energy and the Stark energy-shift of the bound polarons in quantum wires.

Stark effect of donor impurity states in strained heterojunctions under pressure

A modified variational method is adopted to investigate the binding energies of the shallow impurity states near the interface of a strained GaN/AlxGa1-xN heterojunction by using a simplified coherent potential approximation. The relations between the impurity binding energies and pressure, the impurity position, electric field strength and the Al components are calculated for strained zinc-blende GaN/AlxGa1-xN heterojunctions with (001) and (111) orientations respectively. The result indicates that the binding energy of impurity state nearly linearly increases with pressure. The Stark effect on the binding energy as a function of electric field shows blue or red shift in the spectra for different impurity positions. The results corresponding to (001) and (111) orientations are compared. It is found that the effect on the binding energy of Al component is obvious. For an impurity located in the channel side and comparatively far from the interface, a monotonic increase of the binding energies will appear with increasing Al content due to the stronger two-dimensional properties of the electrons, and pressure enhances the increase of amplitude. Whereas for an impurity located in the barrier side, the increase of Al content will weaken the bound between the impurity and the electron to decrease the binding energy.

Binding energy of impurity states in an inverse parabolic quantum well under magnetic field

We have investigated the effects of the magnetic field which is directed perpendicular to the well on the binding energy of the hydrogenic impurities in an inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The Al concentration at the barriers was always x max = 0.3 . The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and donor impurity binding energy in IPQW strongly depends on the magnetic field, Al concentration at the well center and well dimensions.

Binding energy of impurity states in a parabolic quantum dot in a strong magnetic field

AbstractThe binding energies of shallow hydrogenic impurities in parabolic quantum dots are calculated using a variational approach within the effective mass approximation. Results are obtained for CdMnTe/CdMnTe structures as a function of the dot radius in an external magnetic field. The results show that the impurity binding energy (i) increases with the decrease in dot radius, (ii) decreases when the magnetic field is increased for a given dot and (iii) increases to a maximum value at 90 Å and then decreases as the size of the dot increases beyond 90 Å in the finite barrier case. This feature is different from non magnetic quantum well structures. Spin polaronic shifts are estimated using a mean field theory. The results show that the shifts are ≤1 meV in the zero‐field case and still smaller in a magnetic field. This shift not only decreases in a magnetic field but also decreases when the dot radius increases. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of hydrostatic pressure on binding energy of impurity states in spherical quantum dots

The binding energy of shallow hydrogenic impurities in spherical quantum dots in the influence of pressure is calculated using a variational approach within the effective mass approximation. The binding energy is computed for GaAs/Ga 1− x Al x As structures as a function of the dot size. The results show that the impurity binding energy (i) increases with the reduction in dot sizes for a given pressure (ii) increases with the pressure is increased for a given dot (iii) the energy increases to a maximum value at 50 Å and then decreases as the size of the dot increases beyond 50 Å when the realistic model is considered and (iv) the ionization energies are higher as the pressure becomes stronger. All the calculations have been carried out with finite and infinite models and the results are compared with available data in the literature.

Tunneling via impurity states related to the X valley in a thin AlAs barrier

Special features corresponding to resonance tunneling of electrons from the Γ valley of GaAs to the X valley of AlAs were observed in the current-voltage characteristics of single-barrier GaAs/AlAs/GaAs heterostructures. Tunneling both via the states related to the two-dimensional X xy and X z subbands and via the related impurity states was detected. It is shown that the energy position of such impurity states is largely controlled by two factors: (i) spatial confinement of the AlAs layer, which influences both the size-quantization energy levels of the X xy and X z subbands and the corresponding binding energies of impurity states, and (ii) the biaxial compression of the AlAs layer due to a mismatch of the AlAs and GaAs lattice parameters, which results in the splitting of the X xy and X z valleys. This made it possible to determine directly the binding energy of the impurity states; this energy was found to be ∼50 meV for the X z valley and ∼70 meV for the X xy valley.

Binding Energy of Impurity States in Spherical GaAs-Ga1-xAlxAs Quantum Dots

The binding energy of a shallow hydrogenic impurity in spherical GaAs-Ga 1-x Al x As quantum dots is calculated following a variational and a perturbation method. A finite confining potential well with depth determined by the discontinuity of the band gap in the quantum dot and the embedding material is used. We also calculate the binding energy for a dot with infinite confining potential. The calculated energies are computed as functions of both the radius of the dot and the location of the impurity within the dot. The results show that as the dot radius decreases, the impurity binding energy increases for the infinite potential well. On the other hand, for the finite potential well, it reaches a peak value and then diminishes to a limiting value corresponding to the radius for which there are no bound states in the well. The results obtained by the perturbation method are almost similar in nature but differ to some degree from those obtained by the variational method.

Binding Energy of Impurity States in Spherical GaAs–Ga1xAlxAs Quantum Dots

The binding energy of a shallow hydrogenic impurity in spherical GaAs–Ga1–xAlxAs quantum dots is calculated following a variational and a perturbation method. A finite confining potential well with depth determined by the discontinuity of the band gap in the quantum dot and the embedding material is used. We also calculate the binding energy for a dot with infinite confining potential. The calculated energies are computed as functions of both the radius of the dot and the location of the impurity within the dot. The results show that as the dot radius decreases, the impurity binding energy increases for the infinite potential well. On the other hand, for the finite potential well, it reaches a peak value and then diminishes to a limiting value corresponding to the radius for which there are no bound states in the well. The results obtained by the perturbation method are almost similar in nature but differ to some degree from those obtained by the variational method.

Binding energy of impurity states in spherical quantum dots with parabolic confinement

The binding energy of shallow hydrogenic impurities in spherical quantum dots (QDs) with parabolic confinement is calculated, using a variational approach within the effective mass approximation. The binding energy is computed for GaAs QD as a function of the dot size for different impurity positions, and also as a function of the impurity position for different dot sizes. The results show that the impurity binding energy increases with the reduction in the dot dimension. The binding energy is also found to depend on the location of the impurity, and the same is the maximum for the on-center impurity.

Controlled modulation of the binding energy of impurity states in a quantum-well system

Controlled modulation of the binding energy of impurity states in a quantum-well system

Управляемая модуляция энергии связи примесных состояний в системе квантовых ям

Управляемая модуляция энергии связи примесных состояний в системе квантовых ям