Investigation of iodine as a donor in MBE grown Hg1−xCdxTe

N-type Hg_1−xCd_xTe layers with x values of 0.3 and 0.7 have been grown by molecular beam epitaxy using iodine in the form of CdI₂ as a dopant. Carrier concentrations up to 1.1 × 10¹⁸ cm⁻³ have been achieved for x = 0.7 and up to 7.6 × 10¹⁷ cm⁻³ for x=0.3. The best low temperature mobilities are 460 cm²/(Vs) and 1.2 × 10⁵ cm²/(Vs) for x=0.7 and x=0.3, respectively. Using CdI₂ as the dopant modulation doped HgTe quantum well structures have been grown. These structures display very pronounced Shubnikov-de Haas oscillations and quantum Hall plateaus. Electron densities in the 2D electron gas in the HgTe quantum well could be varied from 1.9 × 10¹¹ cm⁻² up to 1.4 × 10¹² cm⁻² by adjusting the thicknesses of the spacer and doped layer. Typical mobilities of the 2D electron gas are of the order of 5.0 × 10⁴ cm²/(Vs) with the highest value being 7.8 × 10⁴ cm²/(Vs).     

MBE growth and properties of ZnO on sapphire and SiC substrates

Molecular beam epitaxy (MBE) of ZnO on both sapphire and SiC substrates has been demonstrated. ZnO was used as a buffer layer for the epitaxial growth of GaN. ZnO is a würtzite crystal with a close lattice match (<2% mismatch) to GaN, an energy gap of 3.3 eV at room temperature, a low predicted conduction band offset to both GaN and SiC, and high electron conductivity. ZnO is relatively soft compared to the nitride semiconductors and is expected to act as a compliant buffer layer. Inductively coupled radio frequency plasma sources were used to generate active beams of nitrogen and oxygen for MBE growth. Characterization of the oxygen plasma by optical emission spectroscopy clearly indicated significant dissociation of O₂ into atomic oxygen. Reflected high energy electron diffraction (RHEED) of the ZnO growth surface showed a two-dimensional growth. ZnO layers had n-type carrier concentration of 9 × 10¹⁸ cm⁻³ with an electron mobility of 260 cm²/V-s. Initial I-V measurements displayed ohmic behavior across the SiC/ZnO and the ZnO/GaN heterointerfaces. RHEED of GaN growth by MBE on the ZnO buffer layers also exhibited a two-dimensional growth. We have demonstrated the viability of using ZnO as a buffer layer for the MBE growth of GaN.     

Preparation and properties of CuInS2 thin film prepared from electroplated precursor

Thin CuInS₂ films were prepared by sulfurization of Cu/In bi-layers. First, the precursor layer was electroplated onto the treated surface of Mo-coated glass. Observation of the cross-section prepared by focused ion beam (FIB) etching revealed that the void-free film was initially formed on the top surface of the precursor layer and continued to grow until the advancing front of the film reached the Mo layer. The nucleation of voids near the bottom of the CuInS₂ film followed. To determine whether the condition of the Cu/In alloy influences the CuInS₂ quality we investigated the Cu/In alloy state using FIB. We found that the annealed precursor of low Cu/In ratio (1.2) has several voids in the mid position in the layer compared with Cu-rich precursor (1.6). The cross-sectional view of the Cu-rich absorber layer is uniform compared with the low copper absorber layer. Thin film solar cells were fabricated using the CuInS₂ film (Cu/In ratio: 1.2) as an optical absorber layer. It was found that the optimization of a sulfurization period is important in order to improve the cell efficiency. We have not yet obtained good results with high Cu-rich absorber because of a blister problem. This blister was found before sulfurization. So, we are going to solve this blister problem before sulfurization.     

竖向荷载作用下墙梁的弹塑性分析

通过分析总结近年来国内外对砖砌体的本构关系和破坏准则的理论研究成果,找出了较合理、适用的本构关系和破坏准则的组合,能较好地描述墙梁受力破坏的力学特性。并基于塑性理论,编制了“墙梁结构弹塑性有限元法计算程序”,对一些算例进行了验算,得到较好的结果。采用对比分析和图表显示的方法,得出在竖向荷载作用下,随着弹塑性的发展,墙体竖向压应力的变化规律。     

"蜂窝状腹板刚性梁"的设计和制造

"蜂窝状腹板刚性梁"是一种再生式梁,以其自重轻,工艺简单,具有较好的经济性等优点,被国内外技术人员广泛采用。参考了国内外的资料,并在青岛三联金属结构集团公司进行试制,于2002年在国产30万机组的水平刚性梁中首先采用,获得较好的经济效益。     

双曲结构VFDF雷达干扰宽带多波束形成技术

采用一种高效的双曲结构可变分数延时滤波器（V FD F ）实现了宽带波束形成,可以在不改变滤波器系数的情况下改变波束指向,并采用这种可变分数延时滤波器实现了雷达干扰宽带多波束形成,通过共用子滤波器减小了硬件开销。     

SOI亚微米波导光栅的设计与制作

报道了SOI基亚微米小尺寸波导光栅器件的设计、制作与测试结果。提出了波导与光栅同步制作的方案,避免了套刻,节约了成本。实验中采用电子束光刻(EBL)、感应耦合等离子体(ICP)刻蚀等先进半导体工艺技术,结合图形补偿等技术手段,完成了亚微米波导光栅的制作。光栅周期为350nm,占空比16∶19。采用该光栅做反射镜,制作了法布里-珀罗(F-P)谐振腔,经测试得到了与模拟相吻合的结果,峰谷比达到11dB。     

协作多点传输系统有限反馈下容量分析

协作多点传输（Coordinated Multiple Point,CoMP）是围绕IMT Advanced的目标而提出的。它通过基站内不同射频接入点（RRU）协作、基站和其所属Relay协作及基站间协作等多种多点协作方式,以减小小区边缘干扰,提高小区边缘频谱效率,增加有效覆盖。这里在有限反馈信道下研究了如何使频谱效率最大化,并分3种情况进行容量分析,包括了在最大SNR波束成型、波束成型信道容量的上界,以及极端情况下的波束成型。     

Monte Carlo Simulation of Damage Depth in Focused Ion Beam Milling Si3N4 Thin Film

The damage properties of Focused Ion Beam（FIB） milling Si3N4 thin film are investigated by the detailed analyzing images of nanoholes and simulation of Monte Carlo. The damage depth in the Si3N4 thin film for two different ion species（Gallium and Arsenic） under various parameters（ion energy, angle of incidence） are investigated by Monte Carlo method. The simulations show the damage depth increases with the increasing ion energy, the damage depth is dependent on the angle of incident ion, the curves of the damage depth for Ga ion and As ion at 30 keV nearly superpose, while the damage depth for Ga with 90 keV ion is more than that for As ion with the same energy.     

利用LCD相位调制获得高效率空心光束

空心光束由于具有一系列特殊物理性质,所以它在对微观粒子的三维操控技术中占据了极其重要的地位.本文提出采用LCD对入射激光进行相位调制得到高衍射效率空心光束的方法.文章研究了螺旋波的特性,分析了LCD相位调制的原理,在LCD上作出螺旋波的实时纯相位图对入射光进行相位调制,获得具有高衍射效率的空心光束.实验结果表明,采用LCD相位调制方法产生空心光束不但具有实时可调,方便、精确的优点,还具备高衍射效率.