Enhanced Thermoelectric Performance of Non-equilibrium Synthesized Fe0.4Co3.6Sb12-xGex Skutterudites via Randomly Distributed Multi-scaled Impurity Dots

The p-type Ge doped Fe0.4Co3.6Sb12-xGex skutterudites with multi-scaled impurity dots（500 nm-2 mm） were successfully prepared by using melt-quenching（MQ） and subsequent spark plasma sintering（SPS） technique. Compared with traditional method, the new technology significantly shortened the processing time from several days to less than 24 hours. The phase of impurity dots was demonstrated to be CoSb through analysis of X-ray diffraction（XRD） and energy-dispersive spectrum（EDS）. Impurity dots were induced by Ge substitution of Sb in the non-equilibrium synthesized process. Due to the abandonment of the long reaction of annealing crystallization, a few of Ge atoms would fail to substitute Sb site of skutterudite in this non-equilibrium synthesized process, leading to that the multi-scaled impurity dots randomly distributed in the matrix of skutterudite Fe0.4Co3.6Sb12-xGex. The combination of multi-scaled impurity dots scattering long wavelength heat-carrying phonons and the point defect scattering short and middle wavelength heat-carrying phonons dramatically made the 22.2% reduction of lattice thermal conductivity. As a result, compared with unsubstituted sample of Fe0.4Co3.6Sb12, the maximum ZT value was increased by 30.5%. Thus, the two marked features of this new synthesis process, the shortened preparation time and the enhanced thermoelectric performance, would make a promising commercial application in the future.

The binding energy of a hydrogenic impurity in self-assembled double quantum dots

The binding energy of a hydrogenic impurity in self-assembled double quantum dots is calculated via the finitedifference method. The variation in binding energy with donor position, structure parameters and external magnetic field is studied in detail. The results found are： （i） the binding energy has a complex behaviour due to coupling between the two dots; （ii） the binding energy is much larger when the donor is placed in the centre of one dot than in other positions; and （iii） the external magnetic field has different effects on the binding energy for different quantum-dot sizes or lateral confinements.

Quantum entanglement transition in vertically coupled two single-electron quantum dots with charged impurity

Effects of a charged impurity on the ground state of two vertically coupled identical single-electron quantum dots with and without applied magnetic field are investigated. In the absence of the magnetic field, the investigations of the charged impurity effect on the quantum entanglement (QE) in some low-lying states are carried out. It is found that, both the positive charged impurity (PCI) and the negative charged impurity (NCI) reduce the QE in the low-lying states under consideration except that the QE in the ground state is enhanced by the NCI. Additionally, in the domain of B from 0 Tesla to 15 Tesla, the ground state energy E, the ground state angular momentum L and the ground state QE entropy S are worked out. As far as the ground state are concerned, the PCI (NCI) blocks (induces) the angular momentum phase transition and the QE phase transition besides the known fact (i.e., the PCI/NCI decreases/increases the energy) in the magnetic field.

Simultaneous Effects of Hydrostatic Pressure and Conduction Band Non-parabolicity on Binding Energies and Diamagnetic Susceptibility of a Hydrogenic Impurity in Spherical Quantum Dots

与在中心上 hydrogenic 杂质的抗磁的危险性一起的 1S， 2S，和 2P 状态的有约束力的精力上的传导乐队 non-parabolicity 和静水力学的压力的同时的效果在典型 GaAs/AlxGa1xAs 球形的量点限制了理论上用矩阵 diagonalization 方法被调查。在这方面，乐队 non-parabolicity 的效果用 LuttingerKohn 有效集体方程被执行了。有约束力的精力和 hydrogenic 杂质的抗磁的危险性面对传导乐队 non-parabolicity 效果作为点半径的一个函数和压力的不同的值被计算。结果我们到达了如下：乐队边 non-parabolicity 的加入增加有约束力的精力和减少为一个给定的压力和半径的抗磁的危险性的绝对值；有约束力的精力增加和有增加压力的抗磁的危险性还原剂的大小。

Impurity-related electronic properties in quantum dots under electric and magnetic fields

This paper presents a systematic study of the ground-state binding energies of a hydrogenic impurity in quantura dots subjected to external electric and magnetic fields. The quantum dot is modeled by superposing a lateral parabolic potential, a Gaussian potential and the energies are calculated via the finite-difference method within the effectivemass approximation. The variation of the binding energy with the lateral confinement, external field, position of the impurity, and quantum-size is studied in detail. All these factors lead to complicated binding energies of the donor, and the following results are found： （1） the binding energies of the donor increase with the increasing magnetic strength and lateral confinement, and reduce with the increasing electric strength and the dot size; （2） there is a maximum value of the binding energies as the impurity placed in different positions along the z direction; （3） the electric field destroys the symmetric behaviour of the donor binding energies as the position of the impurity.

Polarizabilities of Impurity Doped Quantum Dots under Pulsed Field: Role of Additive White Noise

We make a rigorous exploration of the profiles of a few diagonal and off-diagonal components of linear (αxx, αyy, αxy andαyx), first nonlinear (βxxx, βyyy, βxyy andβyxx), and second nonlinear (γxxxx, γyyyy, γxxyyandγyyxx) polarizabilities of quantum dots under the influence of external pulsed field. Simultaneous presence of additive white noise has also been considered. The quantum dot contains dopant described by a Gaussian potential. The numbers of pulse and the dopant location have been found to fabricate the said profiles jointly. The β components display greater complexity in their profiles in comparison with the α and γ counterparts. The presence of noise prominently enhances the influence of dopant coordinate on the polarizability profiles, particularly for α and γ components. However, for β components, the said influence becomes quite evident both in the presence and absence of additive noise. The study reveals some means of achieving stable, enhanced, and often maximized output of noise-driven linear and nonlinear polarizabilities.

Effects of Impurity on the Ground—State Transitions of a Quantum Dot in Strong Magnetic Field

The low-lying spectra of parabolic quantum dots with or without an impurity at the center are investigated. While it has been known that the electron-electron interaction leads to ground-state transitions on magic values of angular momentum in a magnetic field. We show, in this paper, that the implantation of an impurity ion at the center can either enhance or suppress such transitions, depending on whether it is an acceptor or a donor ion.

Thermoelectric transport through a quantum dot with a magnetic impurity

We study the thermoelectric effect in a small quantum dot with a magnetic impurity in the Coulomb blockade regime. The electrical conductance, thermal conductance, thermopower, and the thermoelectrical figure of merit （FOM） are calcu- lated by using Green＇s function method. It is found that the peaks in the electrical conductance are split by the exchange coupling between the electron entering into the dot and the magnetic impurity inside the dot, accompanied by the decrease in the height of peaks. As a result, the resonances in the thermoelectric quantities, such as the thermal conductance, ther- mopower, and the FOM, are all split, opening some effective new working regions. Despite of the significant reduction in the height of the electrical conductance peaks induced by the exchange coupling, the values of the FOM and the ther-mopower can be as large as those in the case of zero exchange coupling. We also find that the thermoelectric efficiency, characterized by the magnitude of the FOM, can be enhanced by adjusting the left-right asymmetry of the electrode-dot coupling or by optimizing the system＇s temperature.

H_2^+-Like Impurities Confined by Spherical Quantum Dots:a Candidate for Charge Qubits

We have calculated the electron energy of the ground and lower excited states for H_2^+-like impurity statesconfined in finite spherical quantum dots in GaAs.Based on the characteristics of energy levels,we have proposed ascheme for realizing charge qubit composed by the the ground and the first excited states of this confined double donorsystem for the first time.In the proposed scheme the charge qubit is coded in terms of the located electronic states.

Weakly Coupled Three—Layer Quantum Dot with a Charged Impurity in Magnetie Field

The states of a weakly coupled 3-quantum-dot system with an external charged impurity located on the z-axis are studied in a magnetic field.The evolutions of the true ground state with the magnetic field B are botained for various impurity cases.It is found that the negative charge impurity would promote the phase transition of the true ground state.

Effects of built-in electric field and donor impurity on linear and nonlinear optical properties of wurtzite InxGa1-xN/GaN nanostructures

The linear and nonlinear optical absorption coefficients(ACs)and refraction index changes(RICs)of 1s-1p,1p-1d,and 1f-1d transitions are investigated in a wurtzite InxGa1-xN/GaN core-shell quantum dot(CSQD)with donor impurity by using density matrix approach.The effects of built-in electric field(BEF),ternary mixed crystal(TMC),impurity,and CSQD size are studied in detail.The finite element method is used to calculate the ground and excited energy state energy and wave function.The results reveal that the BEF has a great influence on the linear,nonlinear,and total ACs and RICs.The presence of impurity leads the resonant peaks of the ACs and RICs to be blue-shifted for all transitions,especially for 1s-1p transition.It is also found that the resonant peaks of the ACs and RICs present a red shift with In-composition decreasing or core radius increasing.Moreover,the amplitudes of the ACs and RICs are strongly affected by the incident optical intensity.The absorption saturation is more sensitive without the impurity than with the impurity,and the appearance of absorption saturation requires a larger incident optical intensity when considering the BEF.

Linear and Nonlinear Optical Properties of Spherical Quantum Dots:Effects of Hydrogenic Impurity and Conduction Band Non-Parabolicity

Simultaneous effects of an on-center hydrogenic impurity and band edge non-parabolicity on intersubband optical absorption coefficients and refractive index changes of a typical GaAs/Al x Ga 1 x As spherical quantum dot are theoretically investigated,using the Luttinger-Kohn effective mass equation.So,electronic structure and optical properties of the system are studied by means of the matrix diagonalization technique and compact density matrix approach,respectively.Finally,effects of an impurity,band edge non-parabolicity,incident light intensity and the dot size on the linear,the third-order nonlinear and the total optical absorption coefficients and refractive index changes are investigated.Our results indicate that,the magnitudes of these optical quantities increase and their peaks shift to higher energies as the influences of the impurity and the band edge non-parabolicity are considered.Moreover,incident light intensity and the dot size have considerable effects on the optical absorption coefficients and refractive index changes.

Effect of an impurity on 3-electron quantum dots in magnetic fields

The ground-state property of a 2-dimensional 3-electron quantum dot (QD) subjected to an external magnetic field B and affected by an impurity is studied. The impurity is located at the z-axis by a distance d from the plane of the dot. The evolution of the angular momentum L0 and the spin S0 of the ground state in accordance with B and d has been calculated, and the results are summarized and plotted in a (L0, S0) diagram. The spatial distribution of the electrons (the size and the geometric features) and the optical absorption have also been investigated. The (L0, S0) diagram indicates that L0 and S0 may jump when d and/or B vary. It was found that, due to the constraints arising from symmetry, each symmetric geometry is accessible only to a specific group of states having specific L0 and S0.

Spectrum and Binding Energy of an Off-Center Hydrogenic Donor in a Spherical Quantum Dot

Off-center impurity effects in a spherical quantum dot are theoretically studied by degenerate perturbationmethod in strong confinement.The energy levels and binding energies are computed for the typical GaAs material asfunction of the donor position.The numerical results show the quantum size effect.We note that the energy levels andbinding energies are not only related to the position of donor and the strength of confinement,but also related to thefold of degenerate states.We can see obviously that gaps will appear among the degenerate states and the splitting ofenergy levels and binding energies will appear as the position of the impurity is shifted away off the center.

磁场对正方体量子点中类氢杂质束缚能的影响

利用有效质量近似 ,计算了磁场影响下正方体量子点中类氢杂质体系的束缚能 ;与相同条件下量子线以及球形量子点的束缚能进行了比较 ,得出合理的结果 ;

磁场和杂质对二维3电子量子点基态的影响

使用少体物理方法 ,计算了在不同的磁场、杂质作用下二维 3电子量子点基态的能量和角动量 ,获得了它们受磁场和杂质影响的结果 ,并且从动力学和对称性两方面对结果进行了分析。

内建电场和杂质对双电子柱形量子点系统束缚能的影响

在有效质量近似下,采用变分法,研究了内建电场和杂质对双电子柱形GaN/Al_rGa_(1-x)N量子点系统束缚能的影响。结果表明:杂质带负电时,体系基态能量都比较大,不易形成稳定的束缚态。带电量为e的施主杂质位于量子点中心时,杂质电子的束缚能随量子点高度和半径的增加先缓慢增大后减小,存在最大值;随着Al含量的增加,体系的束缚能增大。随着杂质从量子点下界面沿z轴移至上界面,体系的束缚能先增大后减小。与单电子杂质态相比,内建电场对双电子量子点系统束缚能的影响比较显著;当量子点高度L<6 nm时,杂质双电子量子点系统的束缚能大于单电子杂质态束缚能,而当量子点高度L>6 nm时,杂质双电子量子点系统的束缚能小于单电子杂质态束缚能。

Ge/Si量子点的生长研究进展

要有效应用SK模式生长的Ge量子点,必须实现Ge量子点的位置可控并且进一步缩小Ge量子点的尺寸。阐释了这方面的研究进展,特别对图形衬底生长Ge量子点,利用Si表面的自组织性在错切割的邻晶面衬底上生长有序Ge岛,表面杂质诱导成岛这三个方面的进展加以介绍分析。

纤锌矿GaN柱形量子点中类氢施主杂质态

在有效质量近似和变分原理的基础上,选取含两个变分参数的波函数,研究了纤锌矿结构的GaN/AlxGa1-xN单量子点中类氢施主杂质体系的结合能随量子点(QD)尺寸以及杂质在量子点中位置的变化,并与以前使用不同尝试波函数的计算结果进行了比较。结果表明:由我们选取的两变分参数波函数得到的结果与前人选取的两变分参数波函数得到的结果相比有所改进,而与选取一个变分参数波函数得到的结果一致。同时我们还计算了体系的维里定理值随量子点半径的变化情况,所得结果与前人工作结果一致,说明本文选取的两变分参数波函数能很好地描述柱形量子点中施主杂质态的运动。

杂质对柱形量子点系统束缚能的影响

在有效质量近似和变分原理的基础上,考虑内建电场(BEF)效应和量子点的三维约束效应,研究了纤锌矿结构的GaN/AlxGa1-xN单量子点中杂质体系的基态能量与杂质电荷的关系,讨论了杂质电子的束缚能随量子点的主要结构参数(量子点高度L和量子点半径R)以及杂质在量子点中不同位置的变化规律,并研究了考虑量子点内外电子有效质量失配对杂质电子束缚能的影响.