变分方法研究ZnO量子点中激子的基态特性

ZnO是一种新型宽禁带直接带隙Ⅱ-Ⅵ族半导体材料,室温激子束缚能高达60meV,远大于室温热离化能(26meV),因此ZnO是适于室温或更高温度下使用的高效紫外光电材料。ZnO半导体量子点材料与体材料相比具有崭新的光电特性,特别在紫外激光器件方面,与ZnO的激子特性密切相关,因此理论上对ZnO量子点中激子的基态特性进行研究就显得十分必要。采用有效质量近似(EMA)方法,提出新的比较简单的尝试波函数,对ZnO量子点中激子的基态特性进行了计算。计算结果与实验结果基本吻合,说明我们的计算结果比较真实、有效。对变分参数K_e、K_h,归一化常数N_e、N_h以及波函数ψ随粒径变化关系进行了计算。计算结果表明,当量子点半径较小(r≤4.0a_B)时,激子的波函数ψ变化非常迅速,而由于此时量子点具有很大的比表面积,因此量子点所处的环境、体内的缺陷、杂质会对其产生非常强烈的影响,同时其表面(界面)的介质会对其基态特性产生影响,因此对量子点进行有效的修饰与掺杂以减少其表面缺陷及表面悬键,减少无辐射复合与界面发射是非常必要的。     

透镜型量子点中类氢杂质基态能的计算

通过有效质量近似和变分法，研究了垂直磁场下透镜型量子点中类氢杂质基态能量，并与球型量子点进行了比较.研究表明：对于球型量子点，基态能仅与杂质的偏离距离有关，与垂直和水平偏离无关；而对于透镜型量子点，由于水平方向和垂直方向束缚势的非对称性，电子基态能不仅与杂质的偏离距离有关，还与杂质偏离方向有关. 关键词： 透镜型量子点 基态能 变分法     

半导体束缚激子基态能的变尺度法

提出了计算体系基态能的变尺度法，用该算法计算了电子和空穴有效质 量比值不同时，离子化施主束缚激子（D+，X）的基态能. 在求解体系基态能上与传统的变分法相比有很大的优势，尤其适合复杂体系基态能的计算. 关键词： 束缚激子 氦原子 基态能 变尺度方法     

垂直耦合自组织InAs双量子点中激子能的计算

在有效质量近似条件下研究了垂直耦合的自组织InAs/GaAs量子点的激子态.在绝热近似条件下，采用传递矩阵方法计算了电子和空穴的能谱.通过哈密顿量矩阵的对角化，对电子和空穴间的库仑相互作用进行了精确处理.讨论了两量子点间的垂直距离对激子基态能的影响.从基态波函数概率分布的角度，讨论了激子的束缚能.计算了重空穴和轻空穴激子的基态能随外部垂直磁场变化的函数关系.计算了量子点大小（量子点半径）对激子能的影响. 关键词： 量子点 激子 对角化     

利用B-splines特性计算PbS量子点中的激子基态能量的量子尺寸效应

利用B-splines特性构建量子点中激子的波函数,计算PbS量子点中激子的基态能量E_g的量子尺寸效应,并将计算结果与实验结果及其他理论计算结果进行比较;利用B-splines技术计算的激子的基态能量在整个区域与实验完全符合,同时计算了有效质量和势垒高度对基态能量E_g的量子尺寸效应的影响.     

计算双电子原子基态能量的坐标张弛变分法

给出了一种计算双电子原子基态能量和波函数的坐标张弛的变分方法.同时,利用Matlab语言开发了一个软件程序,对He原子和类He离子的基态能量进行了变分计算.     

球型核壳量子点结构中二类激子向一类激子的转化

在有效质量近似下,采用变分方法研究了球型核壳量子点中激子的性质。数值计算了电子波函数随位置的变化关系以及临界势随球壳宽度和核半径的比值的变化关系。结果表明,当球壳宽度和核半径的比值为给定值时,存在一临界势,当局域势减小到临界势时,激子从二类激子转化为一类激子;当局域势为给定值时,存在一临界比值,当球壳宽度和核半径的比值减小到临界比值时,激子亦从二类激子转化为一类激子。该结果对研究球型核壳量子点中的电子结构有参考价值。     

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。     

类氦原子体系基态能量的变分法数值研究

选取由指数形式函数的线性组合所构成的试探波函数,利用变分法对类氦原子体系的基态能量进行了数值计算,计算中利用拟牛顿法求非线性方程组的一组实根,计算结果与实验值相当接近．计算表明：当n由1增大到2时,能量的计算值有较大的改进,但由于选取的变分波函数没有考虑到电子关联作用,所以计算只能达到一定的精确度．     

ZnO薄膜的激子能量和束缚能的计算

采用有效质量近似，将耦合在一起的6×6价带本征方程分开来考虑, 取激子试探波函数为z方向和x-y平面分离的形式，用变分法计算了ZnO薄膜重空穴带激子基态能、第一激发态能、束缚能和激子的半径随薄膜厚度的变化关系，并讨论了电子波函数的量子隧穿效应对厚度d<2.0 nm薄膜的能量修正. 关键词： 激子 ZnO薄膜 纤锌矿     

Simulated Annealing for Ground State Energy of Ionized Donor Bound Excitons in Semiconductors

We present a global optimization method, called the simulated annealing, to the ground state energies of excitons. The proposed method does not require the partial derivatives with respect to each variational parameter or solving an eigenequation, so the present method is simpler in software programming than the variational method,and overcomes the major difficulties. The ground state energies of ionized-donor-bound excitons (D , X) have been calculated variationally for all values of effective electron-to-hole mass ratio σ. They are compared with those obtained by the variational method. The results obtained demonstrate that the proposed method is simple, accurate, and has more advantages than the traditional methods in calculation.     

Simulated Annealing for Ground State Energy of Ionized Donor Bound Excitons in Semiconductors

We present a global optimization method, called the simulated annealing, to the ground state energies of excitons. The proposed method does not require the partial derivatives with respect to each variational parameter or solving an eigenequation, so the present method is simpler in software programming than the variational method,and overcomes the major difficulties. The ground state energies of ionized-donor-bound excitons (D^ ,X) have beencal culated variationally for all values of effective electron-to-hole mass ratio σ. They are compared with those obtained by the variational method. The results obtained demonstrate that the proposed method is simple, accurate, and has more advantages than the traditional methods in calculation.     

Energy Spectra of Excitons Bound to a Neutral Acceptor in Quantum Dots

The energy spectra of the ground state for an exciton (X) trapped by a neutral acceptor (A⁰) in a quantum dot with a parabolic confinement have been calculated as a function of the electron-to-hole mass ratio σ by using the hyperspherical coordinates. We find that the (A⁰,X) complex confined in a quantum dot has in general a larger binding energy than those in a two-dimensional quantum well and a three-dimensional bulk semiconductor, and the binding energy decreases with the increase of the electron-to-hole mass ratio.     

电场调控下不对称耦合量子点中激子的发光特性

使用有效质量模型,从理论上对GaAs/A10.35Ga0.65As不对称耦合量子点在不同耦合强度下束缚态和反束缚态的能级分裂情况进行了详细分析,重点探讨了电子和空穴的耦合隧穿对量子点体系能级特征及激子发光强度的影响.研究发现:不对称耦合量子点在外电场作用下价带束缚态和反束缚态能级出现反交现象,反交处的能级分裂值和临界电...     

Ground State Transitions in Vertically Coupled Four-Layer Single Electron Quantum Dots

We study a four-electron system in a vertically coupled four-layer quantum dot under a magnetic field by the exact diagonalization of the Hamiltonian matrix. We find that discontinuous ground-state energy transitions are induced by an external magnetic field. We find that dot-dot distance and electron-electron interaction strongly affect the low-lying states of the coupled quantum dots. The inter-dot correlation leads to some sequences of possible disappearances of ground state transitions, which are present for uncoupled dots.     

Ground State Transitions in Vertically Coupled Four-Layer Single Electron Quantum Dots

We study a four-electron system in a vertically coupled four-layer quantum dot under a magnetic field by the exact diagonalization of the Hamiltonian matrix. We find that discontinuous ground-state energy transitions are induced by an external magnetic field. We find that dot-dot distance and electron-electron interaction strongly affect the low-lying states of the coupled quantum dots. The inter-dot correlation leads to some sequences of possible disappearances of ground state transitions, which are present for uncoupled dots.     

量子力学基态能量计算的改进蚁群优化算法

为进一步减少迭代次数和改善解的质量,对蚁群优化方法进行改进.在求解体系基态能上与传统的变分法相比有很大的优势.求解了氦原子基态能量,并应用于不同半径量子点中砷化镓类氢施主基态能量的计算.通过与变分法和遗传算法的比较,展示了算法的性能.     

Binding Energy of Excitons in a Quantum Ring

The binding energy of excitons confined to a quantum ring under the influence of perpendicular homogeneous magnetic field is calculated as a function of the ring radius. Calculations are made by using the method of exact diagonalization within the effective-mass approximation. The feature of binding energy of the ground state as a function of the ring radius for several values of the magnetic field has been revealed. The interesting feature of our study is that, in a quantum ring, the geometric structure of exeitons may reveal transition.