共查询到20条相似文献,搜索用时 46 毫秒
1.
2.
A variational approach is used to study the ground state of a bound polaron in a spherical quantum dot under an external electric field. The binding energy of the hydrogenic impurity state is calculated by taking the interaction of an electron with both the confined longitudinal optical phonons and the surface optical phonons into account. The interaction between impurity and longitudinal optical phonons has also been considered to obtain the binding energy of a bound polaron. It shows that the polaron effects give significant corrections to the binding energy and its Stark energy shift. The external electric field increases the phonon contributions to the binding energy. 相似文献
3.
4.
R. L. Rodríguez Surez A. Matos-Abiague 《Physica E: Low-dimensional Systems and Nanostructures》2003,18(4):485-491
Polaron effects in asymmetric GaAs-Ga1−xAlxAs quantum wells (QWs) are investigated within the framework of the fractional-dimensional space approach and by using second-order perturbation theory. A well-width dependence of the polaron corrections with a dip and a peak is obtained for both symmetric and asymmetric QWs. The dip and the peak occur in the case of asymmetric QWs for larger well widths than in the case of symmetric QWs. An enhancement of the contrast between the dip and the peak of the polaron energy shift is found for the case of asymmetric QWs. These results show the convenience of using asymmetric QWs instead of symmetric ones in any experimental attempt of detecting the dip and the peak of the polaron energy shift. 相似文献
5.
A bound polaron in a spherical quantum dot 总被引:12,自引:0,他引:12
H.-J. Xie C.-Y. Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):215-218
The binding energy of a bound polaron in a spherical quantum dot has been investigated by using the variational method. The
influence of LO and SO phonons have taken into consideration. Result shows that the phonon contribution to the binding energy
is dependent on the size of the quantum dot as well as the position of the impurity in the quantum dot. Numerical calculation
on the ZnSe quantum dot shows that such contribution is about 5% to 20% of the total binding energy.
Received: 13 October 1997 / Revised: 4 March 1998 / Accepted: 26 May 1998 相似文献
6.
L. Shi 《Solid State Communications》2011,151(24):1907-1911
In the framework of perturbation theory, a variational method is used to study the ground state of a donor bound exciton in a weakly prolate GaAs/Ga1−xAlxAs ellipsoidal finite-potential quantum dot under hydrostatic pressure. The analytic expressions for the Hamiltonian of the system have been obtained and the binding energy of the bound exciton is calculated. The results show that the binding energy decreases as the symmetry of the dot shape reduces. The pressure and Al concentration have a considerable influence on the bound exciton. The binding energy increases monotonically as the pressure or Al concentration increases, and the influence of pressure or Al concentration is more pronounced for small quantum dot size. 相似文献
7.
8.
In this paper, we intend to study the effect of variable mass on the binding energy. In
this regard, we apply an analytic expression for position-dependent effective mass in a
cubic quantum dot. Then, we obtain the binding energies of a shallow donor in the quantum
dot of GaAs/Al
x
Ga1−x
As using a
variational procedure within the effective mass approximation. Calculations are presented
with a constant effective mass and position-dependent effective mass. It is found that (i)
the binding energy decreases as the dot length increases in both the cases of constant and
variable masses, (ii) an increase of binding energy is observed when the spatially varying
mass is included, and (v) the binding energy shows complicated behavior when the
position-dependent mass is included for the small dot size
L ≤ 130 ?. 相似文献
9.
10.
We have proposed the Hamiltonian of the single or double polaron bound to a helium-type donor impurity in semiconductor quantum wells (QWs) in the case of positively charged donor center and neutral donor center. The couplings of an electron with various phonon modes are considered; in particular, the interaction of the impurity with the various phonon modes is included. We have calculated the binding energy of a bound polaron in Al(xl)Ga1-(xl)As/GaAs/Al(xr)Ga1-(xr) As symmetric and asymmetric QWs. The results are obtained as a function of barrier height (or equivalently of Al concent ration x), well width, and the position of impurity in the QWs. Our numerical calculations show clearly that for a thin well the cumulative effects of the electron-phonon coupling and the impurity-phonon coupling can contribute appreciably to the donor binding energy. The enhancement of polaronic effect is also found in the case of ionized donor. 相似文献
11.
12.
Within the framework of effective mass approximation, the binding energy of a hydrogenic donor impurity in zinc-blende GaN/AlxGa1−xN spherical quantum dot (QD) is investigated using the plane wave basis. The results show that the binding energy is highly dependent on impurity position, QD size, Al content and external field. The binding energy is largest when the donor impurity is located at the centre of the QD and the binding energy of impurity is degenerate for symmetrical positions with respect to the centre of QD without the external electric field. The maximum of the donor binding energy is shifted from the centre of QD and the degenerating energy levels for symmetrical positions with respect to the centre of QD are split in the presence of the external electric field. The binding energy is more sensitive to the external electric field for the larger QD and lower Al content. In addition, the Stark shift of the binding energy is also calculated. 相似文献
13.
14.
15.
The donor bound spin polaron in a Cd1?xMnxTe quantum dot is investigated theoretically. Spin polaronic shifts are estimated using a mean field theory. Magnetization is calculated for various concentrations of Mn2+ ions with the dot sizes. The lowest binding energies in a diluted magnetic semiconductor of a Cd1?xMnxTe quantum dot are also estimated. Using the effective mass approximation, calculations are presented with and without spatial dependent effective masses. It is found that (i) the lowest binding energy decreases with the dot radius (ii) position dependent mass gives larger binding energy for smaller dots (iii) the ionization energy becomes more when spin interaction energy is included (iv) variation of increase in ionization energy is sharper for smaller dots with increase in concentration and (v) the magnetization of Mn subsystem increases when concentration of Mn2+ ions increases and it has appreciable changes for smaller dots. 相似文献
16.
Lei Shi Zu Wei Yan 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(6):1-8
The effects of electric field and size on the electron-phonon interaction with an on-center impurity in a Zn1?x Cd x Se/ZnSe spherical quantum dot are studied, taking into account the interactions with confined, half-space and surface optical phonons. In addition, the interaction between impurity and phonons has also been considered. The results show that the electron-confined, electron-half-space, and electron-surface optical phonon interaction energies are all negative. The electron-confined optical phonon interaction energy is weakened by the electric field, but the electron-half-space and electron-surface optical phonon interaction energies are strengthened by it. In particular, the electron-surface optical phonon interaction depends strongly on the electric field, and it will vanish when the electric field is absent. It is also found that the electron-confined optical phonon interaction and electron-impurity “exchange” interaction energies reach a peak values as the quantum dot radius increases and then gradually decrease, but the electron-half-space optical phonon interaction energy exponentially quickly approaches 0 as the quantum dot radius increases. 相似文献
17.
The effect of longitudinal optical phonon field on the ground state and low lying-excited state energies of a hydrogenic impurity in a Zn1−xCdxSe/ZnSe strained quantum dot is investigated for various Cd content using the Aldrich-Bajaj effective potential. We consider the strain effect considering the internal electric field induced by the spontaneous and piezoelectric polarizations. Calculations have been performed using Bessel function as an orthonormal basis for different confinement potentials of barrier height. Polaron induced photoionization cross section of the hydrogenic impurity in the quantum dot is investigated. We study the oscillator strengths, the linear and third-order nonlinear optical absorption coefficients as a function of incident photon energy for 1s-1p and 1p-1d transitions with and without the polaronic effect. It is observed that the potential taking into account the effects of phonon makes the binding energies more than the obtained results using a Coulomb potential screened by a static dielectric constant and the optical properties of hydrogenic impurity in a quantum dot are strongly affected by the confining potential and the radii. It is also observed that the magnitude of the absorption coefficients increases for the transitions between higher levels with the inclusion of phonon effect. 相似文献
18.
19.
Defect chemical and statistical thermodynamic studies on oxygen nonstoichiometric Nd2 − xSrxNiO4 + δ
Takashi Nakamura Keiji Yashiro Kazuhisa Sato Junichiro Mizusaki 《Solid State Ionics》2009,180(26-27):1406-1413
In order to elucidate how oxygen content changes in Nd2 − xSrxNiO4 + δ (x = 0, 0.2, 0.4), defect chemical and statistical thermodynamic analyses were carried out. The relationship among δ, P(O2), and T were analyzed by a defect equilibrium model. Since Nd2 − xSrxNiO4 + δ shows metal like band conduction at high temperatures, chemical potential of hole is expressed by the integration of the Fermi-Dirac distribution function and the density of state. The nonstoichiometric variation of oxygen content in Nd2 − xSrxNiO4 + δ can be explained by the defect equilibrium model with a regular solution approximation. Partial molar entropy and partial molar enthalpy of oxygen are calculated from the nonstoichiometric data and Gibbs–Helmholtz equation. The relationship among defect structure, defect equilibrium, and thermodynamic quantities is elucidated by the statistical thermodynamic model. Thermodynamic quantities are calculated by the statistical thermodynamic model with the results of defect chemical analysis and compared with those obtained from experimental results. Thermodynamic quantities calculated by the statistical thermodynamic model can explain rough tendency of those obtained from the δ–T–P(O2) relationship. 相似文献
20.
Energy of a bound polaron in a magnetic field in asymmetric polar semiconductor heterostructures 总被引:2,自引:0,他引:2
Zhi-jie Wang Yong-gang Weng Jun-jie Shi Zi-xin Liu Shao-hua Pan 《Zeitschrift für Physik B Condensed Matter》1997,104(2):227-234
In this paper, a new modified Hamiltonian of a polaron bound to a donor impurity in asymmetric step quantum wells (QWs) in the presence of an arbitrary magnetic field is given, in which the coupling of an electron with confined bulk-like LO phonons, half-space LO phonons and interface phonon modes is included. Especially, the interaction of the impurity with all possible optical-phonon modes is also considered. The ionization energy of a bound polaron in a magnetic field for asymmetric step QWs are studied by using a modified Lee-Low-Pines (LLP) variational method. The effects of the finite electronic confinement potential and the subband nonparabolicity are also considered. The relative importance of the donor impurity located at the well and the step is analyzed. Our results show the interaction between the impurity and the phonon field in screening the Coulomb interaction has a significant influence on the binding energy of bound polaron. The influence of subband non-parabolicity is appreciable on the bound polaron effects for the narrow well. The binding energy of bound polaron given in this paper are excellent agreement with the experimental measurement. 相似文献