Crack-free GaN/Si(111) epitaxial layers grown with InAlGaN alloy as compliant interlayer by metalorganic chemical vapor deposition

A new method is demonstrated to be effective in reducing mismatch-induced tensile stress and suppressing the formation of cracks by inserting InAlGaN interlayers during the growth of GaN upon Si (1 1 1) substrate. Compared with GaN film without quaternary interlayer, GaN layer grown on InAlGaN compliant layers shows a five times brighter integrated PL intensity and a (0 0 0 2) High-resolution X-ray diffraction (HRXRD) curve width of 18 arcmin. Its chi(min), derived from Rutherford backscattering spectrometry (RBS), is about 2.0%, which means that the crystalline quality of this layer is very good. Quaternary InAlGaN layers, which are used as buffer layers firstly, can play a compliant role to endure the large mismatch-induced stress and reduce cracks during the growth of GaN epitaxy. The mechanisms leading to crack density reduction are investigated and results show that the phase immiscibility and the weak In-N bond make interlayer to offer tenability in the lattice parameters and release the thermal stress. (c) 2005 Elsevier B.V. All rights reserved.

Crack-free InAlGaN quaternary alloy films grown on Si(111) substrate by metalorganic chemical vapor deposition

Crack-free In0.08Al0.25Ga0.67N quaternary films, with and without thick (> 1.5 mum) high-temperature-GaN (HTGaN) interlayer, have been grown on Si(1 1 1) substrates by a low-pressure metalorganic chemical vapor deposition (MOCVD) system. Mole fractions of In and Al in quaternary alloy layers are determined by Energy dispersive spectroscopy (EDS) and Rutherford backscattering spectrometry (RBS), which are recorded as similar to8% and similar to25-27%, respectively. High-resolution X-ray diffraction (HRXRD) and room temperature photoluminescence (RT-PL) results evidence the film's single crystal structure and the existence of local In- and/or Al-rich regions. Compared with GaN film grwon on Si(1 1 1) substrate, no crack is observed in the quaternary ones. Two explanations are proposed. First, mismatch-induced strain is relaxed significantly due to gradual changes of In concentration. Second, the weak In-N bond is likely to break when the sample is cooled down to the room temperature, which is expected to favor the releasing of thermal stress. (C) 2004 Elsevier B.V. All rights reserved.

Strain analysis of InP/InGaAsP wafer bonded on Si by X-ray double crystalline diffraction

Wafer bonding between p-Si and an n-InP-based InGaAsP multiple quantum well (MQW) wafer was achieved by a direct wafer bonding method. In order to investigate the strain at different annealing temperatures, four pre-bonded pairs were selected, and pair one was annealed at 150 degrees C, pair two at 250 degrees C, pair three at 350 degrees C, and pair four at 450 degrees C, respectively. The macroscopical strains on the bonded epitaxial layer include two parts, namely the internal strain and the strain caused by the mismatching of the crystalline orientation between InP (100) and Si (100). These strains were measured by the X-ray double crystalline diffraction, and theoretical calculations of the longitudinal and perpendicular thermal strains at different annealing temperatures were calculated using the bi-metal thermostats model, both the internal strain and the thermal strain increase with the annealing temperature. Normal thermal stress and the elastic biaxial thermal strain energy were also calculated using this model. (c) 2006 Elsevier B.V. All rights reserved.

Wet etching and infrared absorption of AlN bulk single crystals

The defects and the lattice perfection of an AlN (0001) single crystal grown by the physical vapor transport (PVT) method were investigated by wet etching, X-ray diffraction (XRD), and infrared absorption, respectively. A regular hexagonal etch pit density (EPD) of about 4000 cm~(-2) is observed on the (0001) A1 surface of an AlN single crystal. The EPD exhibits a line array along the slip direction of the wurtzite structure, indicating a quite large thermal stress born by the crystal in the growth process. The XRD full width at half maximum (FWHM) of the single crystal is 35 arcsec, suggesting a good lattice perfection. Pronounced infrared absorption peaks are observed at wave numbers of 1790, 1850, 2000, and 3000 cm~(-1), respectively. These absorptions might relate to impurities O, C, Si and their complexes in AlN single crystals.

Analysis of Si/GaAs Bonding Stresses with the Finite Element Method

In conjunction with ANSYS, we use the finite element method to analyze the bonding stresses of Si/GaAs. We also apply a numerical model to investigate a contour map and the distribution of normal stress,shearing stress,and peeling stress,taking into full consideration the thermal expansion coefficient as a function of temperature. Novel bonding structures are proposed for reducing the effect of thermal stress as compared with conventional structures. Calculations show the validity of this new structure.

A model of dislocations at the interface of the bonded wafers

Wafer bonding is regardless of lattice mismatch in the integration of dissimilar semiconductor materials. This technology differs from the heteroepitaxy mainly in the mechanism of generating dislocations at the interface. A model of dislocations at the bonded interface is proposed in this paper. Edge-like dislocations, which most efficiently relax the strain, are predominant at the bonded interface. But the thermal stress associated with large thermal expansion misfit may drive dislocations away from the bonded interface upon cooling.

Twin and grain boundary in InP: A synchrotron radiation study

Experimentally observed X-ray reflectivity curves show bi-crystal(twin) characteristics. The study revealed that there was defect segregation at the twin boundary. Stress was relaxed at the edge of the boundary. Relaxation of the stress resulted in formation of twin and other defects. As a result of formation of such defects, a defect-free and stress-free zone or low defect density and small stress zone is created around the defects. So a twin model was proposed to explain the experimental results. Stress(mainly thermal stress), chemical stoichiometry deviation and impurities nonhomogeneous distributions are the key factors that cause twins in LEC InP crystal growth. Twins on (111) face in LEC InP crystal were studied. Experimental evidence of above mentioned twin model and suggestions on how to get twin-free LEC InP single crystals will be discussed.

Cloning and expression analysis of a HSP70 gene from Pacific abalone (Haliotis discus hannai)

Heat shock protein 70 (HSP70), the primary member of HSPs that are responsive of thermal stress, is found in all multicellular organisms and functions mostly as molecular chaperon. The inducible HSP70 cDNA cloned from Pacific abalone (Haliotis discus hannai) using rapid amplification of cDNA ends (RACE), was highly homologous to other HSP70 genes. The full-length cDNA of the Pacific abalone HSP70 was 2631 bp, consisting of a 5'-terminal untranslated region (UTR) of 90 bp, a 3'-terminal UTR of 573 by with a canonical polyadenylation signal sequence AATAAA and a poly (A) tail, and an open reading frame of 1968 bp. The HSP70 cDNA encoded a polypeptide of 655 amino acids with an ATPase domain of 382 amino acids, the substrate peptide binding domain of 161 amino acids and a C-terminus domain of 112 amino acids. The temporal expression of HSP70 was measured by semi-quantitative RT-PCR after heat shock and bacterial challenge. Challenge of Pacific abalone with heat shock or the pathogenic bacteria Vibrio anguillarum resulted in a dramatic increase in the expression of HSP70 mRNA level in muscle, followed by a recovery to normal level after 96 h. Unlike the muscle, the levels of HSP70 expression in gills reached the top at 12 h and maintained a relatively high level compared with the control after thermal and bacterial challenge. The upregulated mRNA expression of HSP70 in the abalone following heat shock and infection response indicates that the HSP70 gene is inducible and involved in immune response. (c) 2006 Elsevier Ltd. All rights reserved.

不同基板预热温度对激光金属沉积成形过程温度场的影响

为降低成形过程的热应力,抑制成形过程裂缝的产生,减小成形过程试样和基板的翘曲变形,激光金属沉积成形往往需要进行基板预热,因此研究不同基板预热温度对激光金属沉积成形过程温度场的影响具有非常重要的意义.根据有限元分析中的"单元生死"技术,利用APDL编程建立了基板预热对激光金属沉积成形过程温度场影响的三维多道多层数值模拟模型,详细分析了基板未预热和分别预热到200,300,400,500,600℃时对沉积成形过程温度场和温度梯度的影响.通过中国科学院沈阳自动化研究所自行研制的激光金属沉积成形系统和基板预热系统,在与模拟过程相同的参数下,利用镍基合金粉末在基板未预热和分别预热到300,400,500,560℃时进行了成形试验,试验结果跟数值模拟结果吻合较好.

基板预热温度对激光金属沉积成形零件微观组织的影响

基板预热可以显著降低激光金属沉积成形(laser metal deposition shaping,LMDS)过程的热应力,从而抑制成形过程裂缝的产生,但基板预热温度的高低对成形零件的微观组织有着重要的影响,因此研究不同基板预热温度下激光金属沉积成形零件的微观组织变化规律对基板预热温度的选择具有非常重要的意义.利用中国科学院沈阳自动化研究所自行研制的激光金属沉积成形系统和基板预热系统,采用Ni60A金属粉末在基板未预热和预热到200,300,400,500和600℃时分别进行成形试验.然后利用扫描电子显微镜和能量散射谱仪对成形试件的微观组织进行深入的研究,得到不同基板预热温度对激光金属沉积成形零件微观组织的影响规律,为基板预热温度的优化选择提供了重要参考。

基板预热对激光金属沉积成形过程热应力的影响

为降低沉积过程的热应力,抑制成形过程中裂缝的产生,研究基板预热对激光金属沉积成形(Laser metal deposition shaping,LMDS)过程热应力的影响具有非常重要的意义。根据有限元分析中的"单元生死"思想,利用APDL(ANSYS parametric design language)编程建立多道多层激光金属沉积成形过程的数值模拟模型,深入探讨基板未预热和预热到400℃时对成形过程热应力的影响。计算结果表明,基板预热到400℃可以显著降低成形过程中试样的热应力变化波动性,试样的Von Mises热应力最大值可降低10%左右,其中x方向热应力最大值可降低8.5%左右,z方向热应力最大值可降低8.1%左右。在与模拟过程相同的条件下,利用自行研制的激光金属沉积成形设备进行了成形试验,成形试验的结果与模拟结果基本吻合。

不同基板预热温度对激光金属沉积成形过程热应力影响的研究

研究不同基板预热温度对激光金属沉积成形过程热应力的影响,对于降低成形过程的热应力,抑制成形过程裂缝的产生,减小成形过程试样和基板的翘曲变形具有非常重要的意义。根据有限元分析中的"单元生死"技术,编程建立了基板预热对激光金属沉积成形过程热应力影响的三维多道多层数值模拟模型,详细分析了基板未预热和分别预热到200℃、300℃、400℃、500℃、600℃时对沉积成形过程VonMise’s热应力、X方向、Y方向以及Z方向热应力的影响。在与模拟过程相同的参数下,利用镍基合金粉末分别在基板未预热和分别预热到300℃、400℃、500℃、600℃时进行了成形试验,试验的结果跟数值模拟结果吻合较好。

成矿流体构造动力学研究—以冀西北后沟金矿和山东七宝山金矿为例

Tectonic dynamics of metallogenetic fluids is a new crossed subjects among fluid geology, mineral deposit geology and structural geology, and is one of the major current projects of geosciences. It is mainly focused on structures and tectonic dynamic induced by fluid motion, variation of physical condition of fluids (such as temperature and pressure), and interaction between chemical component of fluids and wall rocks in the crust. It takes features of deformation and metamorphysim, which formed during interaction between fluids and rocks and have been perserved in rocks, as basic research objects. After studying types, orders, distributions and fabrics of these features, and analyzing and testing physical and chemical information from these features by some techniques, it is intended to reconstruct moving process of fluids, dynamics of interaction between fluids and rocks, and dynamics of mineralizations. Three problems of tectonic dynamics of metallogenetic fluids, which have not been paid much attentions before, have been studied and discussed in this report. Three relative topics are including: 1)Double-fracturing induced by thermal stress and pressure of fluids and mineralization of Gold-copper in Breccia Pipe at the Qibaoshan in Shandong Province; 2)Parting structures induced by K-metasomatism in the Hougou area, northwestern Heibei province; 3)Migration mechanism of dissolved mass in Fe&S-rich fluids in Hougou gold deposit in Heibei province. After a synthetical study of two years, the author has made some new processes and progresses. The main new advances can be summaried as the following: 1)Thermal stress of fluids formed by temperature difference between fluids and country rock, during upword migration process of fluids with high temperature and pressure, can make rock to break, and some new fractures, which surfaces were uasally dry, formed. The breccia pipe at the Qibaoshan area in Shandong province has some distinct texture of fluidogenous tectonics, the breccia pipe is caused by double-fracturing induced by thermal stress and pressure, distribution of gold-corpper ore bodies are controlled powerfully by fluidogenous tectonics in the breccia pipe. 2)The author discovered a new kind of parting structures in K-alterated rocks in the northwestern part of Hebei province. The parting structures have some distinct geometry and fabrics, it is originated from the acting and reacting fores caused by K-metasomatism. Namely, the crystallizations of metasomatic K-feldspars are a volume expansion process, it would compress the relict fluid bodies, and the pressures in the relict fluid bodies gathered and increased, when the increased pressure of the fluid relict bodies is bigger than the strength of K-feldspars, the K-feldspars were broken with the strong compression, and the parting structures formed. 3)Space position replacing is a important transport pattern of dissolved mass in Fe&S-rich fluid. In addition, basing on views of tectonic dynamics of metallogenic fluids, and time-space texture of fluid-tectonic-lithogenetic-mineralization of the known gold-corpper mineral deposit and the subvolcanic complex at Qibaoshan area in Shandong province, this report does a detail prodict of position-shape-size of two concealed ore-bearing breccia pipe.

The numerical modelling of multi-physics phenomena: The shape casting process

In this paper a computer simulation tool capable of modelling multi-physics processes in complex geometry has been developed and applied to the casting process. The quest for high-quality complex casting components demanded by the aerospace and automobile industries, requires more precise numerical modelling techniques and one that need to be generic and modular in its approach to modelling multi-processes problems. For such a computer model to be successful in shape casting, the complete casting process needs to be addressed, the major events being:-• Filling of hot liquid metal into a cavity mould • Solidification and latent heat evolution of liquid metal • Convection currents generated in liquid metal by thermal gradients • Deformation of cast and stress development in solidified metal • Macroscopic porosity formation The above phenomena combines the analysis of fluid flow, heat transfer, change of phase and thermal stress development. None of these events can be treated in isolation as they inexorably interact with each other in a complex way. Also conditions such as design of running system, location of feeders and chills, moulding materials and types of boundary conditions can all affect on the final cast quality and must be appropriately represented in the model.