Pressure effect on the electron mobility in AlAs/GaAs quantum wells

By taking the influence of optical phonon modes into account, this paper adopts the dielectric continuum phonon model and force balance equation to investigate the electronic mobility parallel to the interfaces for AlAs/GaAs semiconductor quantum wells （QWs） under hydrostatic pressure. The scattering from confined phonon modes, interface phonon modes and half-space phonon modes are analysed and the dominant scattering mechanisms in wide and narrow QWs are presented. The temperature dependence of the electronic mobility is also studied in the temperature range of optical phonon scattering being available. It is shown that the electronic mobility reduces obviously as pressure increases from 0 to 4GPa, the confined longitudinal optical （LO） phonon modes play an important role in wide QWs, whereas the interface optical phonon modes are dominant in narrow QWs, the half-space LO phonon modes hardly influence the electronic mobility expect for very narrow QWs.

The robustness of the quantum spin Hall effect to the thickness fluctuation in HgTe quantum wells

The quantum spin Hall effect （QSHE） was first realized in HgTe quantum wells （QWs）, which remain the only known two-dimensional topological insulator so far. In this paper, we have systematically studied the effect of the thickness fluctuation of HgTe QWs on the QSHE. We start with the case of constant mass with random distributions, and reveal that the disordered system can be well described by a virtual uniform QW with an effective mass when the number of components is small. When the number is infinite and corresponds to the real fluctuation, we find that the QSHE is not only robust, but also can be generated by relatively strong fluctuation. Our results imply that the thickness fluctuation does not cause backscattering, and the QSHE is robust to it.

Analysis of localization effect in blue-violet light emitting InGaN/GaN multiple quantum wells with different well widths

Four blue-violet light emitting InGaN/GaN multiple quantum well（MQW） structures with different well widths are grown by metal–organic chemical vapor deposition. The carrier localization effect in these samples is investigated mainly by temperature-dependent photoluminescence measurements. It is found that the localization effect is enhanced as the well width increases from 1.8 nm to 3.6 nm in our experiments. The temperature induced PL peak blueshift and linewidth variation increase with increasing well width, implying that a greater amplitude of potential fluctuation as well as more localization states exist in wider wells. In addition, it is noted that the broadening of the PL spectra always occurs mainly on the low-energy side of the PL spectra due to the temperature-induced band-gap shrinkage, while in the case of the widest well, a large extension of the spectral curve also occurs in the high energy sides due to the existence of more shallow localized centers.

Effects of a prestrained InGaN interlayer on the emission properties of InGaN/GaN multiple quantum wells in a laser diode structure

The electroluminescence （EL） and photoluminescence （PL） spectra of InGaN/GaN multiple quantum wells （MQWs） with a prestrained InGaN interlayer in a laser diode structure are investigated. When the injection current increases from 5 mA to 50 mA, the blueshift of the EL emission peak is 1 meV for the prestrained sample and 23 meV for a control sample with the conventional structure. Also, the internal quantum efficiency and the EL intensity at the injection current of 20 mA are increased by 71% and 65% respectively by inserting the prestrained InGaN interlayer. The reduced blueshift and the enhanced emission are attributed mainly to the reduced quantum-confined Stark effect （QCSE） in the prestrained sample. Such attributions are supported by the theoretical simulation results, which reveal the smaller piezoelectric field and the enhanced overlap of electron and hole wave functions in the prestrained sample. Therefore, the prestrained InGaN interlayer contributes to strain relaxation in the MQW layer and enhancement of light emission due to the reduction of QCSE.

Tunable resonant radiation force exerted on semiconductor quantum well nanostructures: Nonlocal effects

Resonant radiation force exerted on a semiconductor quantum well nanostructure （QWNS） from intersubband transition of electrons is investigated by taking the nonlocal coupling between the polarizability of electrons and applied optical fields into account for two kinds of polarized states. The numerical results show the spatial nonlocality of optical response can induce the spectral peak position of the exerted force to have a blueshift, which is sensitively dependent on the polarized state and the QWNS width. It is also demonstrated that resonant radiation force is controllable by the polarization and incident directions of applied light waves. This work provides effective methods for controlling optical force and manipulating nano-objects, and observing radiation forces in experiment. This nonlocal interaction mechanism can also be used to probe and predominate internal quantum properties of nanostructures, and to manipulate collective behavior of nano-objects.

Nonlocal effect on resonant radiation force exerted on semiconductor coupled quantum well nanostructures

Based on the microscopic nonlocal optical response theory, the resonant radiation force exerted on a semiconductorcoupled quantum well nanostructure(CQWN), induced by the nonlocal interaction between lasers and electrons in conduction bands, is investigated for two different polarized states. The numerical results show that the spatial nonlocality of optical response can cause a radiation shift(blue-shift) for the spectrum of the resonant radiation force, which is dependent on the CQWN width ratio, the barrier height, and polarized states sensitively. It is also confirmed that the resonant radiation force is steerable by the incident and polarized directions of incident light. This work may provide an advantageous method for detecting internal quantum properties of nanostructures, and open novel and raising possibilities for optical manipulation of nano-objects using laser-induced radiation force.

Optimizing effective phase modulation in coupled double quantum well Mach–Zehnder modulators

We report optimal phase modulation based on enhanced electro–optic effects in a Mach–Zehnder（MZ） modulator constructed by AlGaAs/GaAs coupled double quantum well（CDQW） waveguides with optical gain. The net change of refractive indexes between two arms of the CDQW MZ modulator is derived by both the electronic polarization method and the normal-surface method. The numerical results show that very large refractive index change over 10^（-1） can be obtained, making the phase modulation in the CDQW MZ modulator very highly efficient. It is desirable and important that a very small voltage-length product for π phase shift, V_π× L_0= 0.0226 V · mm, is obtained by optimizing bias electric field and CDQW structural parameters, which is about seven times smaller than that in single quantum-well MZ modulators.These properties open an avenue for CDQW nanostructures in device applications such as electro–optical switches and phase modulators.

Effects of Band Nonparabolicity and Band Offset on the Electron Gas Properties in InAs/AlSb Quantum Well

One-band effective mass model is used to simulation of electron gas properties in quantum well. We calculate of dispersion curves for first three subbands. Calculation results of Fermi energy, effective mass at Fermi level as function of electron concentration are presented. The obtained results are good agreement with the experimental dates.

On the binding energies of excitons in polar quantum well structures in a weak electric field

The binding energies of excitons in quantum well structures subjected to an applied uniform electric field by taking into account the exciton longitudinal optical phonon interaction is calculated. The binding energies and corresponding Stark shifts for Ⅲ-Ⅴ and Ⅱ-Ⅵ compound semiconductor quantum well structures have been numerically computed. The results for GaAs/A1GaAs and ZnCdSe/ZnSe quantum wells are given and discussed. Theoretical results show that the exciton-phonon coupling reduces both the exciton binding energies and the Stark shifts by screening the Coulomb interaction. This effect is observable experimentally and cannot be neglected.

Photoluminescence properties of blue and green multiple InGaN/GaN quantum wells

The photoluminescence(PL) properties of blue multiple InGaN/GaN quantum well(BMQW) and green multiple InGaN/GaN quantum well(GMQW) formed on a single sapphire substrate are investigated. The results indicate that the peak energy of GMQW-related emission(PG) exhibits more significant "S-shaped" dependence on temperature than that of BMQW-related emission(PB), and the excitation power-dependent carrier-scattering effect is observed only in the PG emission;the excitation power-dependent total blue-shift(narrowing) of peak position(line-width) for the PGemission is more significant than that for the PBemission;the GMQW shows a lower internal quantum efficiency than the BMQW. All of these results can be attributed to the fact that the GMQW has higher indium content than the BMQW due to its lower growth temperature and late growth, and the higher indium content in the GMQW induces a more significant compositional fluctuation, a stronger quantum confined Stark effect, and more non-radiative centers.

Optical response of an inverted InAs/GaSb quantum well in an in-plane magnetic field

The optical response of an inverted InAs/GaSb quantum well is studied theoretically. The influence of an in-plane magnetic field that is applied parallel to the quantum well is considered. This in-plane magnetic field will induce a dynamical polarization even when the electric field component of the external optical field is parallel to the quantum well.The electron-electron interaction in the quantum well system will lead to the de-polarization effect. This effect is found to be important and is taken into account in the calculation of the optical response. It is found that the main feature in the frequency dependence of the velocity-velocity correlation function remains when the velocity considered is parallel to the in-plane magnetic field. When the direction of the velocity is perpendicular to the in-plane magnetic field, the depolarization effect will suppress the oscillatory behavior in the corresponding velocity-velocity correlation function. The in-plane magnetic field can change the band structure of the quantum well drastically from a gapped semiconductor to a no-gapped semi-metal, but it is found that the distribution of the velocity matrix elements or the optical transition matrix elements in the wave vector space has the same two-tadpole topology.

Effect of hydrostatic pressure and polaronic mass of the binding energy in a spherical quantum dot

Simultaneous effect of hydrostatic pressure and polaronic mass on the binding energies of the ground and excited states of an on-center hydrogenic impurity confined in a GaAs/GaA1As spherical quantum dot are theoretically investigated by the variational method within the effective mass approximation. The binding energy is calculated as a function of dot radius and pressure. Our findings proved that the hydrostatic pressure led to the decrease of confined energy and the increase of donor binding energy. Conduction band non-parabolicity and the polaron masses are effective in the donor binding energy which is significant for narrow dots not in the confined energy. The maximum donor binding energy achieved by the polaronic mass in the ground and excited states are 2%-19% for the narrow dots. The confined and donor binding energies approach zero as the dot size approaches infinity.

多量子阱钙钛矿半导体合成及光伏性能表征的综合实验设计

随着全球能源需求的持续增长和环境保护意识的加强,开发和利用可再生能源成为了当务之急。在这一背景下,钙钛矿光伏电池以其高效率和低成本的特性受到了广泛研究。本文介绍了一个综合物理实验,即多量子阱钙钛矿的合成及其光伏性能的表征。实验旨在通过合成多量子阱钙钛矿材料并评估其在光伏应用中的性能,以培养学生的科研兴趣和实践技能。实验内容包括:多量子阱钙钛矿材料的合成,采用层间插层策略引入不同尺寸的有机阳离子,以调控材料的结构与相分布;通过X射线衍射和吸收-发光光谱技术对材料的晶体结构、结晶性、光学和电学性质进行表征;制备钙钛矿光伏电池并通过电流-电压曲线评估其光电转换效率。本实验有望使学生深入理解材料物理、器件物理和光伏技术的基本概念,激发他们在新能源领域的研究兴趣,为他们未来的科研活动或职业生涯提供实践经验和技术基础。实验的设计兼顾了教学的全面性和科研的前沿性,有望在物理及相关学科的教学改革中起到积极作用。

Ge/SiGe非对称耦合量子阱强度调制特性仿真

硅基光子学已被广泛认为是能实现片上光电子集成的有效平台,然而迄今为止,对硅基光源、探测器以及调制器等硅基有源器件的研究仍然具有一定的挑战性。为此,提出并仿真分析了一种可以用于实现硅基强度调制的Ge/SiGe非对称耦合量子阱结构。首先,利用8带k·p理论模型对耦合量子阱的能带结构和电子波函数进行了仿真计算;然后,详细分析了外加电场强度在0 kV/cm至60 kV/cm范围内,非对称耦合量子阱对TE和TM偏振模式的传输光的光吸收谱随外加电场强度的变化。仿真结果表明,对于TE偏振模式的传输光,在无外加电场强度条件下,非对称耦合量子阱的第一个吸收带边约在1449 nm处;而在30 kV/cm外加电场下,该量子阱的吸收带边相比于无外加电场情况向长波方向移动约22 nm,比相同外加电压下的普通量子阱显著。本工作所提出的Ge/SiGe非对称耦合量子阱结构是一种有望实现更低工作电压、更高速和更低损耗硅基强度调制器的结构。

将21世纪诺奖实验引入大学物理实验教学——LED中的量子斯塔克效应

目前大学物理实验中所涉及的诺贝尔物理学奖实验多为20世纪的经典实验.百年经典诺奖的实用价值和教育意义已被实践验证.为了深入探索最新诺奖成果的教育价值,使大学生的实验教学与时俱进,与前沿研究接轨,本文将2014年的发光二极管(LED)诺奖实验引入大学物理实验.首先,使学生掌握可见光LED中的多量子阱结构及其发光机理.重点追踪中村修二获奖后对LED的更深入研究,通过对LED发光光谱随注入电流变化的研究,向学生直观展示LED中的量子限制斯塔克效应,并计算出量子阱中压电电场的强度.

Quantum Standing Waves and Tunneling Through a Finite Range Potential

We consider a time independent one dimensional finite range and repulsive constant potential barrier between two impenetrable walls. For a nonrelativistic massive particle projected towards the potential with energies less than the barrier and irrespective of the spatial positioning of the potential allowing for quantum tunneling, analytically we solve the corresponding Schrodinger equation. For a set of suitable parameters utilizing Mathematica we display the wave functions along with their associated probabilities for the entire region. We investigate the sensitivity of the probability distributions as a function of the potential range and display a gallery of our analysis. We extend our analysis for bound state particles confined within constant attractive potentials.

量子卡诺热机有效功率优化

建立了一个以广义势阱中的两个费米子为工质的量子卡诺热机循环模型。导出了循环的功率、效率、有效功率等性能参数的表达式,研究了热漏系数与势阱宽度比对循环性能的影响。结果表明:在不同势阱条件下,功率、效率、有效功率均为势阱宽度比的类抛物线函数,功率与有效功率、效率与有效功率的关系曲线均为扭叶型;在相同势阱条件下,热漏系数对功率没有影响,效率与有效功率随热漏系数的增大而减小。以有效功率为优化目标时,反映了功率和效率的折中,为了热机有更高的效率而牺牲了部分功率。

深紫外AlGaN基多量子阱结构中载流子辐射复合的局域特征

利用磁控溅射和金属有机化学气相沉积方法在c面蓝宝石衬底上生长了深紫外Al_(0.38)Ga_(0.62)N/Al_(0.55)Ga_(0.45)N多量子阱结构,并对其荧光(PL)谱进行了测量。其PL谱的激发密度依赖性测量结果表明,该量子阱的辐射过程包含了局域载流子的散射、极化场的屏蔽和局域态的填充效应;其PL谱的温度依赖性测量结果则表明,该量子阱的辐射过程包含了局域载流子的弛豫、局域载流子的热激发和自由载流子的常规热化效应。这个现象(即多种辐射复合过程的存在)在低温和弱激发测试条件下尤为显著,并且表现出该量子阱结构具有显著的局域深度非均一性和载流子的局域效果,是浅局域载流子的散射效应和深局域态的载流子填充效应共同作用所致。在较低的温度范围内,随着温度升高,该量子阱的辐射过程是由浅局域载流子的弛豫效应和深局域载流子的热激发效应共同作用的结果。这些行为被归因于阱宽起伏所诱发的局域深度的非均一性和载流子的局域效果。

Quantum spin Hall effect in inverted InAs/GaSb quantum wells

We review the recent experimental progress towards observing quantum spin Hall effect in inverted InAs/GaSb quantum wells （QWs）. Low temperature transport measurements in the hybridization gap show bulk conductivity of a non-trivial origin, while the length and width dependence of con- ductance in this regime show strong evidence for the existence of helical edge modes proposed by Liu et al. [Phys. Rev. Lett., 2008, 100： 236601]. Surprisingly, edge modes persist in spite of compa- rable bulk conduction and show only weak dependence on magnetic field. We elucidate that seeming independence of edge on bulk transport comes due to the disparity in Fermi-wave vectors between the bulk and the edge, leading to a total internal reflection of the edge modes.

Properties of polaron in a triangular quantum well induced by the Rashba effect

The properties of the weakly-coupling bound polaron, considering an influence of Rashba effect, which is brought about by the spin-orbit （SO） interaction, in an semiconductor triangular quantum well （TQW）, have been studied by using the linear combination operator and the unitary transformation methods. We obtain an expression for the ground state energy of the weak-coupling and bound polaron in a TQW as a function of the coupling constant, Coulomb bound potential, and the electron areal density. Our numerical resuks show that the ground state energy of the polaron is composed of four parts, one part is caused by the electrons＇ own energy, the second part is caused by the Rashba effect, the third part occurs because of the Coulomb bound potential, and the last term is induced by the interaction between the electrons and LO phonons. The interactions between the orbit and the spin with different directions have different effects on the ground state energy of the polaron.