Room-temperature direct-bandgap photoluminescence from strain-compensated Ge/SiGe multiple quantum wells on silicon

Strain-compensated Ge/Si_0.15Ge_0.85 multiple quantum wells were grown on an Si_0.1Ge_0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition technology on an n +-Si（001） substrate.Photoluminescence measurements were performed at room temperature,and the quantum confinement effect of the direct-bandgap transitions of a Ge quantum well was observed,which is in good agreement with the calculated results.The luminescence mechanism was discussed by recombination rate analysis and the temperature dependence of the luminescence spectrum.     

Epitaxial evolution on buried cracks in a strain-controlled AlN/GaN superlattice interlayer between AlGaN/GaN multiple quantum wells and a GaN template

Epitaxial evolution of buried cracks in a strain-controlled AlN/GaN superlattice interlayer(IL) grown on GaN template, resulting in crack-free AlGaN/GaN multiple quantum wells(MQW), was investigated. The processes of filling the buried cracks include crack formation in the IL, coalescence from both side walls of the crack, build-up of an MQW-layer hump above the cracks, lateral expansion and merging with the surrounding MQW, and two-dimensional step flow growth.It was confirmed that the filling content in the buried cracks is pure GaN, originating from the deposition of the GaN thin layer directly after the IL. Migration of Ga adatoms into the cracks plays a key role in the filling the buried cracks.     

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.     

Existence and construction of simultaneous cloning machines for mixed states

It is a well-known fact that the no-cloning theorem forbids the creation of identical copies of an arbitrary unknown quantum state.In other words,there does not exist a quantum cloning machine that can clone all quantum states.However,it is possible to clone given quantum states under certain conditions,for instance,k distinct pure states|ψ1,|ψ2,...,|ψk can be cloned simultaneously if and only if they are orthogonal.This paper discusses the existence and construction of simultaneous cloning machines for mixed states.It is proved that k distinct mixed statesρ1,ρ2,...,ρkof the n-dimensional quantum system Cncan be cloned simultaneously,that is,there exists a quantum channel Φ on MnMn and a state Σ in Mn,such that Φ(ρiΣ)=ρiρi for all i,if and only ifρiρj=0(i j).Also,the constructing procedure of the desired simultaneous cloning machine is given.     

Optical vibration modes and electron－phonon interaction in ternary mixed crystals of polar semiconductors

Optical vibrations of the lattice and the electron－phonon interaction in polar ternary mixed crystals are studied in the framework of the continuum model of Born and Huang and the random-element-isodisplacement model. A normal-coordinate system to describe the optical vibration in ternary mixed crystals is correctly adopted to derive a new Fr?hlich-like Hamiltonian for the electron－phonon interaction including the unit-cell volume variation influence. The numerical results for the phonon modes, the electron－phonon coupling constants and the polaronic energies for several typical materials are obtained. It is verified that the nonlinearity of the electron－phonon coupling effects with the composition is essential and the unit-cell volume effects cannot be neglected for most ternary mixed crystals.     

Tunneling-induced ultraslow bright and dark solitons in quantum wells

We show the formation of tunneling-induced ultraslow bright and dark solitons in an asymmetric double-quantumwell structure based on the tunneling induced transparency.In this semiconductor structure,the pump field is replaced by the electron-tunneling coupling,which can be modulated by a static electric field.With appropriate conditions,we demonstrate by modulating the intensity of the static electric field that the interplay between the group velocity dispersion and the self-Kerr nonlinearity results in the generation of dark and bright solitons with ultraslow group velocity.     

三元混晶四层系统的表面和界面声子极化激元

运用改进的无规元素等位移模型和玻恩-黄近似,结合电磁场的麦克斯韦方程和边界条件,研究了真空/极性二元晶体薄膜/极性三元混晶薄膜/极性二元晶体衬底四层系统的表面和界面声子极化激元.以AlxGa1-xAs/GaAs和ZnxCd1-xSe/ZnSe为例,获得了表面和界面声子极化激元模的色散关系以及表面模和界面模的频率随混晶组分和薄膜厚度的变化关系.结果表明,三元混晶四层异质结系统中存在七支表面和界面声子极化激元模,且这七支表面模和界面模的频率随混晶组分和薄膜厚度呈非线性变化,三元混晶的\"单模\"和\"双模\"性也在色散曲线中得到了很好的体现.     

ZnSe/BeTe Ⅱ型量子阱中界面结构对发光特性的影响

报道了具有特殊界面结构(界面包含三个Zn—Te或Te—Zn化学键)的非掺杂ZnSe/BeTe II 型量子阱在低温(5—10 K)条件下的空间间接光致发光(PL)光谱的实验结果. PL光谱显示了一个较弱的双峰结构和较低的线性偏振度,并且这两个峰的线性偏振度相反. 此外,这个PL光谱也强烈地依赖于一个外加电场的变化. 这些结果表明样品的两个发光峰是分别来自两个界面的发光跃迁,并且特殊界面结构降低了空间间接PL的发光效率和线性偏振性,以及界面附近的内秉电场. 随着激发强度的增加,PL谱的高能端发光峰显示了一个关键词：Ⅱ型量子阱光致发光界面结构     

纤锌矿氮化物量子阱中光学声子模的三元混晶效应

本文先比较了几种常用方法(修正的无规元素等位移模型、虚晶近似和简化相干势近似等)对纤锌矿三元混晶体声子频率的拟合结果,再选用与实验数据接近的拟合方法,结合介电连续和单轴晶体模型导出含纤锌矿三元混晶In_xGa_1－xN和Al_xGa_1－xN单量子阱各类光学声子模的色散关系,进一步分析了声子模随组分的变化. 结果表明,修正的无规元素等位移模型对单模性纤锌矿     

Zn1-xCdxS三元混晶的电子结构及光学性质计算与实验验证

基于密度泛函理论的平面波超软赝势法,计算了Zn_1-xCd_xS三元混晶的电子结构和光学性质。计算结果表明,Cd进入ZnS晶格后,禁带宽度变窄,硫空位(V_S)缺陷能级随x值增大逐渐向费米能级移动,在紫外和可见波段的吸收截止波长随着x值增大逐渐红移。采用共沉淀法制备了Zn_1-xCd_xS三元混晶,XRD图谱表明形成了Zn_1-xCd_xS合金相,吸收光谱显示了与理论计算相符的能带和吸收截止边的移动规律,荧光光谱显示与V_S相关的发射峰随x增大逐渐红移,与计算得到的V_S缺陷能级的移动规律相同。     

Hyperspherical Analysis of D- in a Quantum Well

By introducing hyperspherical coordinates and assuming the quasiseparability of the hyperradius R from the angular variables Ω in the wavefunctions, we have solved the SchrSdinger equation for a D- center in two dimensions to obtain the low-lying spectrum. The correlation patterns in these states are visualized.``     

In源流量与Ⅲ族流量之比对InGaN/GaN多量子阱性质的影响

利用x射线三轴晶衍射和光致发光谱研究了生长参数In源流量与Ⅲ族流量之比对InGaN/GaN多量子阱结构缺陷(如位错密度和界面粗糙度)和光致发光的影响.通过对（0002）对称和（1012）非对称联动扫描的每一个卫星峰的ω扫描,分别测量出了多量子阱的螺位错和刃位错平均密度,而界面粗糙度则由（0002）对称衍射的卫星峰半高全宽随级数的变化得出.试验发现多量子阱中的位错密度特别是刃位错密度和界面粗糙度随In源流量与Ⅲ族源流量比值的增加而增加,导致室温下光致发光性质的降低,从而也证明了刃位错在InGaN/GaN关键词：x射线三轴晶衍射界面粗糙度位错InGaN/GaN多量子阱     

量子限制斯达克效应对三角形量子阱吸光特性的影响

本文通过计算量子力学波动方程以及载流子传输特性,哈密顿量的H能谱图和边界条件等的理论方法来分析量子限制斯达克效应对三角形量子阱体系吸收特性的影响,说明了选择合适的量子阱垒层对于提高三角形量子阱吸光率具有重要的意义。     

A novel double quantum well device for THz range frequency detection

A novel device has been proposed which uses a double quantum well structure for the detection of signals in the THz range. The technology for the manufacturing of such devices at this point of time is significantly mature so that such a device may be easily fabricated. The detector frequency may be varied from 10 to 90 THz by changing the well widths from 10 to 30 Å.