双势垒磁性隧道结中量子阱共振隧穿效应的第一性原理理论

磁性隧道结材料中自旋相关的量子阱态所导致的共振隧穿现象具有很重要的研究和应用价值，文章介绍了最近在Fe（001）／MgO／Fe／MgO／Fe双势垒磁性隧道结中存在的量子阱共振隧穿效应的理论研究工作，通过量子阱态的第一性原理的计算以及结合对中间Fe薄膜孤岛结构所导致Coulomb阻塞效应的分析，证实了最近Nozaki等人（Nozaki T et al．Phys．Rev．Lett．，2006，96：027208）实验中得到的振荡效应确实来源于中间Fe层多数自旋电子在Г点处形成的△1对称性的量子阱态．Coulomb阻塞效应的存在正是导致实验中低温下量子阱共振隧穿效应不够明显的主要原因．     

楔形光纤与半导体多量子阱平面光波光路芯片的耦合分析

采用楔形光纤(WSF)实现了与半导体多量子阱(MQW)平面光波光路(PLC)芯片的高效耦合。在多量子阱-平面光波光路前置模斑转换器(SSC)和不加模斑转换器的情况下,用阶梯串联法(SCM)数值模拟并优化设计了楔形光纤-平面光波光路间最佳耦合参量:楔形光纤楔角45°、端面圆柱透镜曲率半径2.5μm、模斑转换器-多量子阱-平面光波光路出射椭圆光斑长半轴3.5μm、纵横比5、楔形光纤-平面光波光路间垂直方向和水平方向无偏移、纵向间距5.5μm。用反向推演法(IDM)实验分析了楔形光纤样品的出射光场,与阶梯串联法(SCM)计算结果相比长轴误差为3.125%,短轴误差为0.8%。建立楔形光纤-平面光波光路-单模光纤(SMF)的耦合实验系统,在1.55μm波长处以单模光纤作为出纤的相同条件下,发现楔形光纤激励入射平面光波光路比单模光纤和锥形透镜光纤(TLF)作为入纤的耦合效率分别提高了24.827 dB和16.22 dB,为多量子阱-平面光波光路芯片尾纤封装技术提供了实验原型。     

MOVPE生长的InGaN/GaN单量子阱的光致发光和光吸收特性

研究了用金属有机物气相外延(MOVPE)法在蓝宝石衬底上生长的In组分浓度保持不变的InGaN/GaN单量子阱结构在室温下的发光特性和光吸收特性.实验结果表明,在InGaN厚度<3nm时,随着样品InGaN势阱层宽度的增加(1nm),光致发光(PL)谱的发光峰值波长出现明显的红移33nm现象,而且发光强度下降8%,谱线半峰全宽(FWHM)展宽,通过对样品的透射、反射光谱研究发现,量子阱层窄(1.5nm)的样品在波长接近红外区时出现无吸收的现象,即R+T达到了100%,而在阱层较宽的样品中没有发现这一现象,对引起这些现象的原因进行了讨论.这些结果有助于开发和优化三族氮化物半导体光电器件的进一步研究工作.     

NPB/Alq3有机量子阱光电特性研究

利用热蒸发的方法制备了有机量子阱发光器件和Alq3单层发光器件,其中NPB(N,N′-Di-[(lnaphthalenyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine)作垒层,Alq3(Tris-(8-quinolinolato) aluminum)作阱层,量子阱结构类似于无机半导体的Ⅱ型量子阱结构.实验发现有机量子阱发光器件结构中存在垒层向阱层的F(o)rster无辐射共振能量转移,具有良好的电流-电压特性,光谱的窄化及蓝移,并且光谱的蓝移程度随电压的增大而逐渐增强.     

An investigation into EMI-induced noise in nanometer multi-quantum well InGaN LEDs

This study investigates the low-frequency noise induced by electromagnetic radiation interference (EMI) in a nanometer multi-quantum well InGaN LED (NMQLED). Theoretical models of the noise spectra and the EMI are constructed. In general, a good agreement is identified between the experimental and theoretical results. Both sets of results reveal that the magnitude of the EMI-induced noise is related to the pulse height, the output load, the parasitic capacitance, the interference frequency and the interference amplitude. It is shown that the harmonic noise increases with an increasing interference amplitude and frequency. The techniques presented in this study provide a systematic approach for obtaining the interference noise and signal-to-noise ratio (SNR) in LEDs and similar wavelength-based semiconductor devices.     

Optimization of facet coating for highly strained InGaAs quantum well lasers operating at 1200 nm

The optical output power of a laser diode can be enhanced by anti-reflection (AR) and high-reflection (HR) facet coatings, respectively, at the front and back facet. AR and HR coatings also serve the purpose of protection and passivation of laser diode facets. In this work, we have designed and optimized a single layer λ/4 thick Al₂O₃ film for the AR coating and a stack of λ/4 thick Al₂O₃/λ/4 thick Si bi-layers for the HR coating for highly strained InGaAs quantum-well edge emitting broad area (BA) laser diodes. Effect of the front and back facet reflectivities on output power of the laser diodes has been studied. The light output versus injected current (L–I characteristics) measurements were carried out on selected devices before and after the facet coatings. We have also carried out the numerical simulation and analysis of L–I characteristics for this particular diode structure. The experimental results have been compared and verified with the numerical simulation.     

正切平方势阱中线性与非线性光学折射率变化的研究

利用正切平方势把电子的Schrodinger方程化为了超几何方程，并用超几何函数严格求解了电子的本征值和本征函数利用量子力学中的密度矩阵算符理论导出了正切平方势阱中的线性与三阶非线性光学折射率的解析表达式计算了该系统中的线性与非线性光学折射率变化的大小，讨论了影响折射率变化因素文章以典型的GaAs/AlGaAs势阱为例作了数值计算,数值计算结果表明，势阱的形状和入射光强对光学折射率的变化有着重要的影响.     

A study on radial directional natural frequency and damping ratio in a vehicle tire

The measurement of radial directional natural frequency and damping ratio in a vehicle tire has been studied. Natural frequencies and damping ratios in the radial direction of various tires, from passenger car tires to truck bus tires, are reported. The radial direction modal parameters of tires subjected to different levels of inflation pressure, have been determined by using a frequency response function method. To obtain the theoretical natural frequency and mode shape, the plane vibration of a tire has been modeled as though it were that of a circular beam. By using the Tielking method that is based on Hamilton’s principle, theoretical results have been determined by considering the rotational velocity, tangential and radial stiffness, radial directional velocity and tension force which is due to tire inflation pressure. The results show that experimental conditions can be considered as the parameters that shift the natural frequency and damping ratio.     

A new well‐balanced Hermite weighted essentially non‐oscillatory scheme for shallow water equations

Hermite weighted essentially non‐oscillatory (HWENO) methods were introduced in the literature, in the context of Euler equations for gas dynamics, to obtain high‐order accuracy schemes characterized by high compactness (e.g. Qiu and Shu, J. Comput. Phys. 2003; 193 :115). For example, classical fifth‐order weighted essentially non‐oscillatory (WENO) reconstructions are based on a five‐cell stencil whereas the corresponding HWENO reconstructions are based on a narrower three‐cell stencil. The compactness of the schemes allows easier treatment of the boundary conditions and of the internal interfaces. To obtain this compactness in HWENO schemes both the conservative variables and their first derivatives are evolved in time, whereas in the original WENO schemes only the conservative variables are evolved. In this work, an HWENO method is applied for the first time to the shallow water equations (SWEs), including the source term due to the bottom slope, to obtain a fourth‐order accurate well‐balanced compact scheme. Time integration is performed by a strong stability preserving the Runge–Kutta method, which is a five‐step and fourth‐order accurate method. Besides the classical SWE, the non‐homogeneous equations describing the time and space evolution of the conservative variable derivatives are considered here. An original, well‐balanced treatment of the source term involved in such equations is developed and tested. Several standard one‐dimensional test cases are used to verify the high‐order accuracy, the C‐property and the good resolution properties of the model. Copyright © 2010 John Wiley & Sons, Ltd.     

A comparison of algainas and InGaAsP-based 1.3 μm semiconductor lasers using high pressure

Abstract

We have compared the effect of hydrostatic pressure on the threshold current, I_th, and lasing energy, E_lase, of 1.3 pm quantum-well devices based upon AlGaInAs and InGaAsP. Whilst we observe a very similar dependence of E_lase on pressure for the two materials, we measure strikingly different variations of I_th. By applying pressure to 1.3 μm InGaAsP lasers, I_th typically decreases by ～ 10% over 1 GPa consistent with the reduction of Auger recombination, which forms ～ 50% of I_th at room temperature. However, for the 1.3 μm AlGaInAs-based lasers, we observe an increase in I_th by ～ 8% over the same pressure range. From these results we conclude that non-radiative recombination accounts for only ～ 20% of I_th in AlGaInAs-based devices. This is in good agreement with previous temperature dependence measurements and shows why AlGaInAs-based devices exhibit a reduced temperature sensitivity of I_th which is very important for telecommunications applications.