Electron–hole transition energy for a spherical quantum dot confined in a nano-cylindrical wire

A single-band constant confining potential is applied to InAs spherical quantum dot confined in a GaAs cylindrical nano-wire to determine the electronic structure. The energy eigenvalues and transition energies are numerically calculated as a function of the dot radius. The calculations were performed within the effective mass approximation, using the finite element method. The effect of both spherical and cylindrical confinement, the size dependence of the ground and first excited state energies for electron and heavy hole and transition energies are reported and compared with experimental and theoretical results in relevant conditions.     

The Polaron Self-Energy in a Parabolic Quantum Dot

Polaronic states in a parabolic quantum dot are investigated by using the second order Rayleigh-Schrödinger perturbation theory. It is shown that the absolute values of the ground state energy correction and the excited state energy correction as well as the relevant transition energies increase with decreasing the size of the quant um dot. The results also indicate that the polaron effects in small quantum dots are stronger than those in the corresponding bulk materials.     

Photoluminescence of charged magneto-excitons in InAs single quantum dots

We calculated the photoluminescence spectra of charged magneto-excitons in single two-dimensional parabolic quantum dots, using an unrestricted Hartree–Fock method. The calculated luminescence spectra explain well the observed red shifts of transition energies of InAs/GaAs single quantum dot by additional electron capture in a dot. The magnetic-field-induced transition of the ground state configuration of trapped electrons causes drastic change in the photoluminescence spectra. The dependence of photoluminescence intensities of charged excitons on the excess energies of photogenerated carriers above the bulk GaAs energy gap is studied phenomenologically, by calculating the steady state electron population probability in a dot.     

纤锌矿GaN/AlxGa1-xN应变柱形量子点中杂质态结合能及其压力效应

考虑应变及流体静压力,在有效质量近似下,利用变分法计算了无限高GaN/Al<,x>Ga<,1-x>N应变柱形量子点中类氢杂质结合能.结果表明,在量子点尺寸较小情况下,应变增加了杂质态结合能;而在量子点尺寸较大情况下,应变降低了杂质态结合能.随着Al摩尔分数的增加,杂质态结合能减小.杂质态结合能随着流体静压力的增加而增大...     

Electron–hole transition in a spherical quantum dot confined at the center of a cylindrical nano-wire: Comparison of isotropic and anisotropic effective mass

Electronic structure of an InAs spherical quantum dot placed at the center of a GaAs cylindrical nano-wire is investigated. The Schrodinger equation within the effective mass approximation is solved and the energy eigenvalues and transition energies are calculated as a function of quantum dot and nano-wire radii using the finite element method. The two types of heavy holes, hhI and hhII, with isotropic and anisotropic effective masses are considered, respectively. The effect of spherical and nano-wire confining potentials, the size of the dot and the nano-wire on ground and first excited state energies of the electron, heavy hole I and heavy hole II are investigated. The results show that the electron and heavy holes energies decrease as the dot and the nano-wire radii increase. The emitted wavelength of transitions between el-hhI and el-hhII are also calculated and compared. The results show that the anisotropy of the effective mass has great effect on the emitted wavelength.     

Intersubband,interband transitions,and optical properties of two vertically coupled hemispherical quantum dots with wetting layers

The electron and heavy hole energy levels of two vertically coupled In As hemispherical quantum dots/wetting layers embedded in a Ga As barrier are calculated numerically. As the radius increases, the electronic energies increase for the small base radii and decrease for the larger ones. The energies decrease as the dot height increases. The intersubband and interband transitions of the system are also studied. For both, a spectral peak position shift to lower energies is seen due to the vertical coupling of dots. The interband transition energy decreases as the dot size increases, decreases for the dot shapes with larger heights, and reaches a minimum for coupled semisphere dots.     

Quantum-Confined Stark Effects in a Single GaN Quantum Dot

Using analytical expressions for the polarization field in GaN quantum dot, and an approximation by separating the potential into a radial and an axial, we investigate theoretically the quantum-confined Stark effects. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. The results show that the electron and hole energy levels and the optical transition energies can cause redshifts for the lateral electric field and blueshifts for the vertical field. The rotational direction of electric field can also change the energy shift.     

压力下GaN/Ga1-xAlxN量子点中杂质态的界面效应

考虑界面处导带弯曲,流体静压力以及有效质量随量子点位置的依赖性,采用变分法以及简化相干势近似,研究了无限高势垒GaN/Ga_1-xAl_xN球形量子点中杂质态的界面效应,计算了杂质态结合能随量子点尺寸、电子面密度以及压力的变化关系。结果表明,结合能随压力的增大呈线性增加的趋势,有效质量位置的依赖性以及导带弯曲对结合能有不容忽视的影响。     

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     

电场中非对称高斯势量子点内极化子量子跃迁的厚度效应

计及量子点厚度下,分别选取抛物势和高斯势描写盘型量子点中电子的横向束缚势和纵向束缚势,采用Pekar类型变分法推导出量子点中极化子的基态和第一激发态能量本征值和本征函数,以此为基础,构造了一个二能级结构,并基于二能级体系理论,讨论了极化子在外电场作用下的量子跃迁问题。结果表明,高斯束缚势比抛物束缚势更能精准反映量子点中真实的束缚势;量子点的厚度对极化子的跃迁几率Q所带来的影响有趣且有实际意义,不可忽略;电声耦合强度α、电场强度F、非对称高斯势的势垒高度V₀和束缚范围L等对极化子的基态与第一激发态能量以及量子跃迁的影响显著;本文的结果有助于探讨利用这些物理量来调控量子点的输运特性和光学性质的途径和方法。     

Hydrostatic pressure and temperature effects on the electronic energy levels of a spherical quantum dot placed at the center of a nano-wire

The effect of pressure and temperature on the electronic structure of an InAs spherical quantum dot located at the center of a GaAs cylindrical nano-wire have been determined using finite element method, within the effective mass approximation. The energy levels and transition energies are numerically calculated as a function of the dot radius, pressure and temperature. It is shown that the pressure and temperature effects are significant and should be considered in the study of low-dimensional semiconducting systems. The results show that; energy levels (i) decrease as the dot radius increases (ii) decrease as the pressure increases and (iii) increase as the temperature increases. For very small dot radii, the energy levels show unusual behavior, such that the energy levels increase as the pressure increases. We also found that the transition energy (i) increases as the dot size decreases (ii) increases as the pressure increases and (iii) decreases as the temperature increases.     

Quantum Transition of Two-Level System in a Parabolic Quantum Dot

The time evolution of the quantum mechanical state of an electron is calculated by using variational method of Pekar type on the condition of electric-LO phonon strong coupling in a parabolic quantum dot. We obtained the eigen energies of the ground state and the first-excited state, the eigen functions of the ground state and the first-excited state this system in a quantum dot may be employed as a two-level quantum system-qubit. The supposition electron is in system’s ground state in the initial time, the electron transit from the ground state to the excited state in presence of an electric field F along the x axis. The results indicate that the electron transition probability and the oscillation period increase with decreasing the electron-LO-phonon coupling constant, increasing the electric field and the confinement length.     

Quantum dots with disorder and interactions: a solvable large-g limit

We analyze the problem of interacting electrons on a ballistic quantum dot with chaotic boundary conditions, where the effective interactions at low energies are characterized by Landau parameters. When the dimensionless conductance g of the dot is large, the disordered interacting problem can be solved in a saddle-point approximation which becomes exact as g --> infinity (as in a large-N theory), leading to a phase transition in each Landau interaction channel. In the weak-coupling phase constant charging and exchange interactions dominate the low-energy physics, while the strong-coupling phase displays a spontaneous distortion of the Fermi surface, smeared out by disorder.     

Optical absorption and refraction index change of a confined exciton in a spherical quantum dot nanostructure

Electronic energies of an exciton confined in a strained Zn_1−x Cd _x Se/ZnSe quantum dot have been computed as a function of dot radius with various Cd content. Calculations have been performed using Bessel function as an orthonormal basis for different confinement potentials of barrier height considering the internal electric field induced by the spontaneous and piezoelectric polarizations. The optical absorption coefficients and the refractive index changes between the ground state (L = 0) and the first excited state (L = 1) are investigated. It is found that the optical properties in the strained ZnCdSe/ZnSe quantum dot are strongly affected by the confinement potentials and the dot radii. The intensity of the total absorption spectra increases for the transition between higher levels. The obtained optical nonlinearity brings out the fact that it should be considered in calculating the optical properties in low dimensional semiconductors especially in quantum dots.     

CdSe/HgSe/CdSe量子点量子阱(QDQW)晶粒的光学性质和电子结构

以CdSe纳米晶体为核,用胶体化学的方法,通过化学替代反应,获得了不同阱层或不同垒层的CdSeHgSeCdSe量子点量子阱(QDQW)晶体.紫外可见光吸收谱研究表明,通过调节QDQW中间HgSe阱层的厚度从0.9nm至0,可以调节QDQW颗粒的带隙从1.8变化至2.1eV,实现QDQW纳米晶体的剪裁.光致荧光(PL)谱研究显示,QDQW形成后,CdSeHgSe纳米颗粒表面态得到钝化,显现出发光强度加强的带边荧光峰.利用有效质量近似模型,对QDQW晶粒内部电子的1s—1s态进行了估算,估算结果总体趋势与实验数据相符 关键词： 量子点量子阱晶体 能带剪裁 加强的带边荧光峰     

Exciton binding energy and the optical absorption coefficient in a strained CdxZn1−xO/ZnO quantum dot

Numerical calculations of the excitonic absorption spectra in a strained Cd_xZn_1?xO/ZnO quantum dot are investigated for various Cd contents. We calculate the quantized energies of the exciton as a function of dot radius for various confinement potentials and thereby the interband emission energy is computed considering the internal electric field induced by the spontaneous and piezoelectric polarizations. The optical absorption as a function of photon energy for different dot radii is discussed. Decrease of exciton binding energy and the corresponding optical band gap with the Cd concentration imply that the confinement of carriers decreases with composition x. The main results show that the confined energies and the transition energies between the excited levels are significant for smaller dots. Non-linearity band gap with the increase in Cd content is observed for smaller dots in the strong confinement region and the magnitude of the absorption spectra increases for the transitions between the higher excited levels.     

Size effects of an exciton–acceptor complex in quantum dots

In this study, a detailed investigation of the size effects of an exciton–acceptor complex in a disc-like quantum dot has been carried out by using the matrix diagonalization method and the compact density-matrix approach. We calculate the binding energy and the oscillator strength of intersubband quantum transition from the ground state into the first excited state as a function of the dot radius. Based on the computed energies and wave functions, the linear, third-order and total optical absorption coefficients as well as the refractive index have been examined between the ground and the first excited states. We find that the all absorption spectra and refractive index changes are strongly affected by the quantum dot size. However, for two cases of a smaller dot and a larger dot, the results of quantum size effects on the optical absorptions are opposite.     

抛物量子点中强耦合磁极化子的性质

采用Pekar类型的变分方法研究了抛物量子点中强耦合磁极化子的基态和激发态的性质。计算了基态和激发态磁极化子的束缚能以及磁极化子的共振频率。讨论了这些量对回旋频率和有效限制强度的依赖关系,以及磁极化子光学声子平均数的性质,结果表明:由于Zeeman劈裂,抛物量子点中磁极化子的回旋共振频率劈裂为两支。基态和激发态磁极化子的束缚能以及磁极化子的共振频率都随回旋频率的增加而增大,随量子点的有效束缚强度的增大而减小。     

Interband optical absorption in a strained CdxZn1−xO/ZnO quantum dot

Numerical calculations of the excitonic absorption spectra in a strained Cd_xZn_1−xO/ZnO quantum dot are investigated for various Cd contents. We calculate the quantized energies of the exciton as a function of dot radius for various confinement potentials and thereby the interband emission energy is computed considering the internal electric field induced by the spontaneous and piezoelectric polarizations. The optical absorption as a function of photon energy for different dot radii is discussed. Decrease of exciton binding energy and the corresponding optical band gap with the Cd concentration imply that the confinement of carriers decreases with composition x. The main results show that the confined energies and the transition energies between the excited levels are significant for smaller dots. Non-linearity band gap with the increase in Cd content is observed for smaller dots in the strong confinement region and the magnitude of the absorption spectra increases for the transitions between the higher excited levels.     

Binding energy of a hydrogenic impurity in a 2D circular quantum dot

The binding energies of hydrogenic impurity states with an impurity atom located at the center of a two-dimensional circular quantum dot confined by an infinite barrier potential are studied as a function of the dot radius and of the screening parameter in the potential. Accurate binding energies are obtained for the 1s, 2s and 2p states by numerical integration of the 2D Schrödinger equation. The binding energies are found to increase with a decrease in the dot radius, and decrease with an increase in the value of the screening parameter q_sin all cases. Further the levels become unbound at a finite value of the dot radius.