Polaronic Effects on the Impurity Binding Energy in a Polar Crystal Slab Within an Electric Field

The effects of the interaction between electron and bulk longitudinal optical (LO) phonon and surface optical (SO) phonon on the impurity binding energy of the ground state in a polar crystal slab within an external electric field are derived by using the method of a variational wavefunction. The binding energy of the bound polaron is obtained as a function of the impurity position, the slab thickness and the electric field strength. It is found that the polaronic correction to the impurity binding energy by the SO phonon may be enhanced and that by the LO phonon may be reduced with increasing electric field strength. And the effect of the electron-phonon interaction is quite important in increasing the values of binding energy.     

Properties of a Bound Polaron under a Perpendicular Magnetic Field

We investigate the influence of a perpendicular magnetic field on a bound polaron near the interface of a polar-polar semiconductor with Rashba effect. The external magnetic field strongly changes the ground state binding energy of the polaron and the Rashba spin-orbit （SO） interaction originating from the inversion asymmetry in the heterostructure splits the ground state binding energy of the bound polaron. In this paper, we have shown how the ground state binding energy will be with the change of the external magnetic field, the location of a single impurity, the wave vector of the electron and the electron areal density, taking into account the SO coupling. Due to the presence of the phonons, whose energy gives negative contribution to the polaron＇s, the spin-splitting states of the bound polaron are more stable, and we find that in the condition of week magnetic field, the Zeeaman effect can be neglected.     

纤锌矿In_(0.19)Ga_(0.81)N/GaN量子阱中光学声子和内建电场对束缚极化子结合能的影响

用改进的Lee-Low-Pines变分方法研究纤锌矿In0.19Ga0.81N/GaN量子阱结构中束缚极化子能量和结合能等问题,给出基态结合能、不同支长波光学声子对能量和结合能的贡献随阱宽和杂质中心位置变化的数值结果.在数值计算中包括了该体系中声子频率的各向异性和内建电场对能量和结合能的影响、以及电子和杂质中心与长波光学声子的相互作用.研究结果表明,In0.19Ga0.81N/GaN量子阱材料中光学声子和内建电场对束缚极化子能量和结合能的贡献很大,它们都引起能量和结合能降低.结合能随着阱宽的增大而单调减小,窄阱中减小的速度快,而宽阱中减小的速度慢.不同支声子对能量和结合能的贡献随着阱宽的变化规律不同.没有内建电场时,窄阱中,定域声子贡献小于界面和半空间声子贡献,而宽阱中,定域声子贡献大于界面和半空间声子贡献.有内建电场时,定域声子贡献变小,而界面和半空间声子贡献变大,声子总贡献也有明显变化.在In0.19Ga0.81N/GaN量子阱中,光学声子对束缚极化子能量和结合能的贡献比GaAs/Al0.19Ga0.81As量子阱中的相应贡献(约3.2—1.8和1.6—0.3 meV)约大一个数量级.阱宽(d=8 nm)不变时,在In0.19Ga0.81N/GaN量子阱中结合能随着杂质中心位置Z0的变大而减小,并减小的速度变快.随着Z0的增大,界面和半空间光学声子对结合能的贡献缓慢减小,而定域光学声子的贡献缓慢增大.     

束缚极化子有效质量的温度特性

采用改进的线性组合算符和幺正变换方法研究强、弱耦合束缚极化子的有效质量的温度特性,对RbCl晶体进行数值计算。结果表明,强耦合束缚极化子的振动频率和有效质量随温度的升高而增加,随库仑势的增加而增大。     

外电场下极性量子阱中杂质态结合能

我们用变分方法研究了外电场下量子阱中的杂质态结合能,计算中既考虑了电子同体纵光学声子和界面光学声子的相互作用又考虑了杂质中心同体纵光学声子和界面光学声子的相互作用。我们以GaAs/Al_0.3Ga_0.7As量子阱为例,讨论了结合能随杂质位置、阱宽和电场强度的变化规律。得到了电子-声子相互作用对杂质态结合能和斯塔克效应的修正是相当明显的。     

Energy of a bound polaron in a magnetic field in asymmetric polar semiconductor heterostructures

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.     

抛物量子阱中束缚极化子的极化势和结合能

利用改进的Lee-Low-Pines(LLP)方法,用变分法计算了无限深抛物量子阱中同时考虑与体纵光学声子和界面纵光学声子相互作用的束缚极化子的极化势和结合能.数值计算得出:阱宽较大时极化势很小,阱宽较小时极化势较大,所以对于较窄的抛物阱必须考虑极化势.对于给定阱宽的抛物阱,随着远离阱中心极化势迅速减小,当到达阱的界面附近极化势又开始增大.阱宽较小时,束缚极化子的结合能随着阱宽L的增大而急剧减小;阱宽较大时,结合能减小的非常缓慢,最后接近体材料中的三维值.     

Bound polaron in a wurtzite GaN/AlxGa1 − xN ellipsoidal finite-potential quantum dot

A variational method is used to study the ground state of a bound polaron in a weakly oblate wurtzite GaN/Al_xGa_1 − xN ellipsoidal quantum dot. The binding energy of the bound polaron is calculated by taking the electron couples with both branches of LO-like and TO-like phonons due to the anisotropic effect into account. The interaction between impurity and phonons has also been considered to obtain the binding energy of a bound polaron. The results show that the binding energy of bound polaron reaches a peak value as the quantum dot radius increases and then diminishes for the finite potential well. We found that the binding energy of bound polaron is reduced by the phonons effect on the impurity states, the contribution of LO-like phonon to the binding energy is dominant, the anisotropic angle and ellipticity influence on the binding energy are small.     

抛物量子点中强耦合束缚极化子的性质

采用Pekar类型的变分方法研究了抛物量子点中强耦合束缚极化子的基态和激发态的性质。计算了束缚极化子的基态和激发态的能量、光学声子平均数。讨论了量子点的有效束缚强度和库仑束缚势对基态能量、激发态能量以及光学声子平均数的影响。数值计算结果表明:量子点中强耦合束缚极化子的基态和激发态能量及光学声子平均数均随量子点的有效束缚强度的增加而减小,基态、激发态能量随库仑束缚势的增加而减小,光学声子平均数随库仑束缚势的增加而增大。     

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.     

The bound polaron in an electric field in polar semiconductor heterostructures

We have calculated the ionization energy of a bound polaron confined in general step quantum wells (QWs) in the presence of an electric field, in which the coupling of an electron with confined bulk-like LO phonons, half-space LO phonons and interface phonons is considered. In particular, the interaction of the impurity with the various phonon modes is also included in QWs. Results have been obtained as a function of the barrier height, the well width, the electric field intensities and the position coordinates of the impurity in the QWs. Our numerical calculations clearly show that the interaction between the impurity and the phonon field plays an important role in screening the Coulomb interaction. It is shown that the cumulative effect of the electron–phonon coupling and the impurity–phonon coupling can contribute appreciably to the donor ionization energy. Only for a certain range of well widths can we neglect all the polaronic effects.     

抛物量子点中强耦合束缚极化子的光学声子平均数

采用线性组合算符和幺正变换方法研究了在库仑场束缚下抛物量子点中强耦合束缚极化子的振动频率和光学声子平均数,并对其进行了数值计算。结果表明:强耦合束缚极化子的振动频率和光学声子平均数随量子点的有效受限长度的增加而减小,随电子-LO声子耦合强度的增强而增加,束缚极化子的振动频率随库仑势的增加而减小。     

Polaron effects on the binding energy of a double donor impurity in quantum wells in an electric field

The binding energy of the single and double bound polaron bound to a helium-type donor impurity in quantum wells (QWs) subject to a perpendicular electric field are calculated by a variational method. The couplings of an electron and the impurity with various phonon modes are considered. The results show that the cumulative effects of the electron–phonon coupling and the impurity–phonon coupling can contribute appreciably to the binding energy for the single bound polaron but only in some severe conditions for the double bound polaron. They also show that the binding energy is sensitive to the electric field strength. The comparison between the binding energies in the case of the impurity placed at the quantum well center and at the quantum well edge is also given.     

量子点中束缚极化子性质的温度依赖性

采用线性组合算符和幺正变换方法研究抛物量子点中弱耦合束缚极化子性质的温度依赖性,导出了弱耦合束缚极化子的振动频率、基态能量和声子平均数随温度的变化关系。取ZnS晶体为例进行数值计算,结果表明:量子点中弱耦合束缚极化子的振动频率、基态能量和声子平均数随温度的升高而增大。     

The phonon effects on the impurity states in cylindrical quantum wire with a finite confining potential

The variational method and the effective mass approximation are applied to calculate the binding energies of the hydrogenic impurity states in a cylindrical quantum wire with finite deep potential well. The phonon effects on the impurity states are considered by taking both the couplings of the electron-phonon and the impurity ion-phonon into account. The numerical results for the GaAs cylindrical quantum wire are given and discussed. It is found that the ion-phonon interaction reduces the impurity binding energy and supplies key contribution to the energy shift, but the electron-phonon coupling enhances the binding energy less. Longitudinal optical (LO) phonons play more important role than interface optical (IO) phonons in the impurity potential screening. The polaron effect caused by LO phonons is more important when the wire is thinner, otherwise the LO phonons are dominant for the thicker wires.     

Polaron effect on the optical rectification in spherical quantum dots with electric field

The polaron effect on the optical rectification in spherical quantum dots with a shallow hydrogenic impurity in the presence of electric field is theoretically investigated by taking into account the interactions of the electrons with both confined and surface optical phonons. Besides, the interaction between impurity and phonons is also considered. Numerical calculations are presented for typical Zn_(1-x)Cd_xSe/ZnSe material. It is found that the polaronic effect or electric field leads to the redshifted resonant peaks of the optical rectification coefficients. It is also found that the peak values of the optical rectification coefficients with the polaronic effect are larger than without the polaronic effect, especially for smaller Cd concentrations or stronger electric field.     

The polaron effect on the binding energy of a shallow donor impurity in quantum-well wires in an electric field

Using a variational technique, the effect of electron-longitudinal optical (LO) phonon interaction on the ground and the first few excited states of a hydrogenic impurity in a semiconductor quantum wire of rectangular cross section under an external electric field is studied theoretically for the impurity atom doped at various positions. The results for the binding energy as well as polaronic correction are obtained as a function of the size of the wire, the applied uniform electric field and the position of the impurity. It is found that the presence of optical phonons changes significantly the values of the impurity binding energies of the system. Taking into account the electron–LO phonon interaction the 1s→2p_y and 1s→2p_z transition energies are calculated as a function of applied electric field for different impurity positions.     

抛物量子点中强耦合束缚磁极化子的声子平均数

采用线性组合算符和幺正变换方法导出了强耦合束缚磁极化子的振动频率和声子平均数。讨论了量子点的有效受限长度、磁场、库仑场和电子-LO声子耦合强度对抛物量子点中强耦合束缚磁极化子振动频率和声子平均数的影响。数值计算结果表明:强耦合束缚磁极化子的振动频率和声子平均数均随量子点的有效受限长度、回旋共振频率的增加而减小,随库仑束缚势的增加而增加,声子平均数随电子-LO声子耦合强度增加而减小。     

量子点中磁激子的极化子效应

采用推广的LLP方法研究了自组织量子点中磁激子的极化子效应。考虑带电粒子和声子的相互作用,得到了激子能量随磁场的变化关系。结果表明,激子-声子的相互作用降低了激子的能量,但影响很小;极化子效应在没有外磁场时较明显,随着外磁场的增加,这种效应变得越来越弱。     

抛物量子点中弱耦合束缚极化子的相互作用能

研究了抛物量子点中弱耦合束缚极化子的性质,采用改进的线性组合算符和幺正变换方法导出了束缚极化子的振动频率、有效质量和相互作用能。讨论了量子点的有效受限长度、电子LO声子耦合强度和库仑场对抛物量子点中弱耦合极化子的振动频率、有效质量和相互作用能的影响。数值计算结果表明:弱耦合束缚极化子的振动频率和相互作用能随有效受限长度的减少而急剧增大,振动频率随库仑势以及电子LO声子耦合强度的增加而增加,而相互作用能随库仑势以及电子LO声子耦合强度的增加而减小。有效质量仅与电子LO声子耦合强度有关。