Fractal processing for an analysis of the quality and resistivity of large semiconductor plates

A nondestructive method is suggested for the analysis of the quality and resistivity inhomogeneity of semiconductor plates in an ionization system with a SI GaAs semiconductor plate. At the same time, a device for rapid visualization and recording the resistance inhomogeneity and photoconductivity distribution throughout the bulk material in high‐resistivity and photosensitive semiconductor plates of large diameter (50‐100 mm) is described. Semiconductor plates with the resistivity from 10⁵ to 10⁹ Ωcm can be analyzed in the proposed device. The possibilities of the device have been evaluated, i.e. a relative change of the resistance inhomogeneity is determined by a relative change of discharge light emission intensity when a current is passed through an ionization cell. For the quantitative analysis of quality and resistivity inhomogeneity of semiconductor plates, fractal dimension analysis was used following the records of the discharge light emission intensity. The quality of plates was analyzed using both the profile and spatial distributed light emission intensity data showing the internal inhomogeneity in the semiconductor plate. Thus, by using fractal concept, the surface quality of the high‐resistivity semiconductor plate can be assessed exactly and the size and location of the internal inhomogeneities in the semiconductor plate to be ascertained. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

双向低触发电压横向晶闸管放电管研究

依据触发电压VS、触发电流IS、维持电流IH及触发电压、维持电流高低温变化率指标要求,利用Silvaco-TCAD半导体器件仿真软件完成了双向低触发电压横向晶闸管(SCR)放电管的设计.详细分析了对触发特性产生显著影响的结构参数(N-衬底区、寄生PNP晶体管P-集电区、寄生NPN晶体管P-基区、N+阴极区、N+触发区、...     

离子轰击对准直碳纳米管生长的影响

利用负偏压增强热丝化学气相沉积系统,在辉光放电的情况下制备出准直碳纳米管,并用扫描电子显微镜研究了不同负偏压对准直碳纳米管生长的影响.结果表明随着负偏压的增大,准直碳纳米管的平均直径减小,平均长度增大.由于辉光放电的产生,在衬底表面附近形成阴极鞘层,以及在阴极鞘层内形成大量的离子和在衬底表面附近形成很强的电场导致了离子对衬底表面的强烈轰击.最后,分析和讨论了离子的轰击对准直碳纳米管生长的影响.     

Identification of the dynamics of plasma‐induced damage in a CuInSe2 thin film by fractal processing

A planar ionization system for rapid visualization and recording the resistance inhomogeneity and photoconductivity distribution in a chalcopyrite‐type semiconductor (CuInSe₂) copper‐indium‐diselenide film is studied. A part of the discharge energy is transferred to the electrodes of the system by the bombardment of the electrode surface due to an electron‐ion flow. This process leads to the sputtering mechanism of the electrode surface material. It is shown that the plasma‐induced damage (PID) in a CuInSe₂ thin film was primarily due to the effectiveness of sputtering and physico‐chemical interactions in the discharge gap during the transition from Townsend to the glow type. At the same time a nondestructive method is suggested for the analysis of the dynamics of PID in the CuInSe₂ thin film by fractal processing in the planar ionization system. Some properties of the device have been evaluated, such as a relative change of the resistance inhomogeneity is determined by a relative change of discharge light emission (DLE) intensity when a current is passed through an ionization cell. For the quantitative analysis of the change in the dynamic feature of PID of CuInSe₂ thin films, fractal dimension analysis was used following the records of the DLE intensity. The quality of the film was analyzed using both the profile and spatial distributed DLE intensities data showing the surface inhomogeneity and damage in the thin film as function of time. Thus, by using fractal concept, the order of the surface damage and the quality of the CuInSe₂ as function of time can be assessed exactly and the size and location of the surface inhomogeneities in thin film to be ascertained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

How to Avoid Plastic Deformation in GaAs Wafers during Molecular Beam Epitaxial Growth

Plastic deformation in two‐inch diameter GaAs wafers resulted from standard thermal treatments which accompanied epitaxial growth in molecular beam epitaxy (MBE) machines of three different makes. Synchrotron based X‐ray transmission topography was used to distinguish between thermal treatment induced dislocation bundles and misfit dislocations. Eradication of the wafer slip related dislocation bundles has been achieved by modifications to the sample holder of a user built MBE machine. These modifications are discussed, the extent of the problem is briefly outlined, and an extrapolation of the susceptibility of GaAs wafers of higher diameters to this type of plastic deformation is given.     

Liquid-phase epitaxy of AlGaAs heterostructures on profiled substrates

A method of fabrication of planar local structures using the selective epitaxial growth of GaAs and AIGaAs layers from liquid phase on profiled GaAs substrates was developed. The planar regrowth of the recesses formed in GaAs substrates by local etching was performed using the anisotropy of epitaxial growth rates and also by providing the uniformity of mass flow to the surface of local epilayer. The developed method of localized structures fabrication was used for improving the characteristics of discrete light emitting diodes — LED and for fabrication of DLE monolithic arrays.     

Light-Induced Instabilities in Photo-Oriented Liquid Crystal Cells

In a planar liquid crystal sample sandwiched between a photosensitive and a reference plate instabilities occurred, when the cell was illuminated from the reference side. The instabilities were induced both by polarized white light source and monochromatic laser beams. Static and dynamic regimes were found; for laser irradiation dynamic instability was found only in a range of polarization directions. A model, developed for monochromatic excitation, predicts that at certain thicknesses dynamic instability is forbidden. Experiments on a wedge-like cell confirmed this conclusion.     

基于单体石墨纤维的场发射特性研究

利用化学气相沉积(CVD)法,以甲烷为碳源在管式炉中合成了单体石墨纤维(MGF)。选取长度为3.426 mm,顶端球面半径为11.26 μm的单体石墨纤维直立于圆铜片上作为阴极,以导电ITO玻璃作为阳极,采用二极管结构在真空室中进行直流场发射测试,证实MGF的开启场强为0.477 5 V/μm。基于有限元仿真软件ANSYS进行电磁场分析,计算了MGF在不同电压下的有效发射面积。结果表明,当电压为5.36 kV时,MGF达到最大发射面积为796.226 μm²,在实验测量电压范围内,平均发射电流密度可以达到46.069 A/cm²,单体石墨纤维具有良好的场发射特性。     

快离子导体Li1.5Y0.5Zr1.5(PO4)3包覆层对富镍三元正极材料电化学性能的影响

研发富镍低钴的先进正极材料是目前提高锂离子电池能量密度和降低电池成本的有效办法。然而,随着Ni含量的增加,富镍层状氧化物普遍存在前驱体合成困难、结构不稳定和界面活性高等一系列问题,阻碍了富镍层状氧化物正极材料的市场化推广。本文采用优化的共沉淀法制备出结构稳定的LiNi_0.8Mn_0.1Co_0.1O₂(NCM811)正极材料,同时在NCM811材料表面均匀包覆快离子导体Li_1.5Y_0.5Zr_1.5(PO₄)₃涂层,以克服富镍层状氧化物界面结构不稳定和易受电解液腐蚀的难题。在4.5 V高截止电压下,改性样品0.2 C的放电比容量为214.2 mAh·g^-1,10 C的放电比容量高达158.8 mAh·g^-1,高于原始样品的203.7 mAh·g^-1(0.2 C)和82.7 mAh·g^-1(10 C)。同时,改性样品在4.3 V下经1 C循环200次后的容量保持率高达84.7%,高于原始样品(61.94%)。     

Electroluminescence in Amorphous Pyrazoline Films Under DC Fields

We have investigated the electroluminescence, EL, behavior in amorphous films of a pyrazoline derivative under dc fields. The current vs. voltage characteristics indicated a space charge limited current behavior with traps distributed exponentially within the forbidden energy gap. EL was detected in the current range of double carrier injection which ocurred after all traps in the sample were filled up. Spectral studies showed that the light emission zone was loalized around the cathode side of the pyrazoline film. The brightness, measured as a function of current, indicated the EL in the lower current density range to be dominated by delayed luminescence.     

Poole‐Frenkel electrical conduction in europium oxide films deposited on Si(100)

Thin Eu₂O₃ films were prepared on Si (P) substrates to form MOS devices. The oxide crystal structure was determined by X‐ray diffraction (XRD). The electrical transport properties of the devices with amorphous and crystalline Eu oxide were investigated. The current‐voltage and current‐temperature characteristics suggest a Poole‐Frenkel (PF) type mechanism of carrier transport through the device when the applied field is more than 105 V/cm. A deviation from PF leakage current course was found and attributed to the current carrier trapping. We have also observed that, the dielectric spectra of MOS structure are different when the insulator is an amorphous or crystalline thin film. From which we calculate the relaxation time (τ) of the interface (insulator/semiconductor) dipoles. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

钠离子电池正极材料磷酸钒钠的研究进展

NASICON型的磷酸钒钠具有三维框架结构,充放电电压平台较高,储能容量大,循环稳定性好,是一种很具前景的钠离子电池正极材料.本文综合了大量磷酸钒钠有关文献的研究成果,介绍了磷酸钒钠的晶体结构与电化学性能,以及磷酸钒钠的常用合成方法与改性手段.目前所进行的研究中,最常见的是以固相法和溶胶凝胶法合成,也包括喷雾干燥法、水热法、静电纺丝法等,改性手段主要包括以不同碳源进行碳包覆、离子掺杂、与导电物质复合以及材料纳米化四种,磷酸钒锂材料在改性后其导电性与电化学性能均有明显提高,这有望推进钠离子电池的实用化进程.     

电铸超薄金刚石刀具的研制及应用

分析了超薄金刚石刀具的研究现状,用电铸工艺制备出金刚石-镍复合膜,探讨了阴极电流密度、搅拌速度和搅拌桨位置、阴极悬挂倾角、镀液温度等电镀工艺参数对金刚石-镍复合膜品质的影响规律;探讨了复合膜的后续加工工艺,指出电火花加工可以有效除去复合膜的毛边和毛刺,是一种行之有效的后续加工方法;研制出了超薄金刚石-镍复合膜切割片,并对其切割性能进行了初步试用研究.     

Numerical modelling of instability and supercritical oscillatory states in a Czochralski model system of oxide melts

The motivation for this study is the need for accurate numerical models of melt flow instabilities during Czochralski growth of oxides. Such instabilities can lead to undesirable spiralling shapes of the bulk crystals produced by the growing process. The oxide melts are characterized by Prandtl numbers in the range 5<Pr <20, which makes the oxide melt flow qualitatively different from the intensively studied flows of semiconductors characterized by smaller Prandtl numbers Pr <0.1. At the same time, these flows can be modelled experimentally by many transparent test fluids (e.g. water, silicon oils, salt melts), which have similar Prandtl numbers, but allow one to avoid the extremely high melting‐point temperatures of the oxide materials. Most previous studies of melt instabilities for Prandtl numbers larger than unity suffer from a lack of accuracy that is caused by the use of coarse grids. Recent convergence studies made for a series of simplified problems and for a hydrodynamic model of Czochralski growth showed that for a second order finite volume method reliable stability results can be obtained on grids having at least 100 nodes in the shortest spatial direction. The obvious numerical difficulties call for an extensive benchmark exercise, which is proposed here on the basis of recently published experimental and numerical data, as well as some preliminary results of this study. The calculations presented are performed by two independent numerical approaches, which are based on second‐order finite volume and finite element discretizations. We start our comparison from the steady states, whose parametric dependencies sometimes exhibit turning points and multiplicity. We then compare the critical temperature differences corresponding to the onset of instability, and finally compare calculated supercritical oscillatory states and phase plots. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of semi-insulating GaAs crystals in low temperature gradients by using the Vapour Pressure Controlled Czochralski Method (VCz)

The present paper gives a review on fundamentals, modelling, growth, structural and electrical properties of semi-insulating GaAs single crystals, grown in low temperature gradients by the Vapour Pressure Controlled Czochralski Method (VCz), with diameters from 75 up to 150 mm. Special attention is drawn to the investigation of the temperature-fields inside the growing crystals (and thus thermoelastic stress). Additionally, the influence of convective transport of heat within meit and inert gas is investigated by both experiment and modelling. Thermodynamic aspects of arsenic pressure control within the inner VCz chamber as well as the special experimental and technological challenges are discussed. High quality 100 mm (4-inch) crystals with EPD < 10⁴ cm⁻² and low as-grown residual strain are presented. Very low carbon concentrations of ≈10¹⁴ cm⁻³ were obtained for the first time in VCz crystals. This material, as one of the challengers to conventional LEC material, is able to meet similar electrical specifications whilst showing improved structural quality and better parameter homogeneity even in the as-grown state. Initial studies of a VCz crystal grown without boric oxide encapsulant is presented.     

Electromigration of Aluminium through Quasi Bamboo‐Like Grain Blocked Silicide Interconnects

MoSi₂ interconnects between electrical aluminium contact pads were exposed to a high direct current density of 1 MA cm^‐2 during 2000 hours. Thermal annealing of the interconnects prior to the experiment generated grains of almost the width of the line, providing for bamboo‐like grain blocked polycrystalline clusters along the line acting as migration stopping sites. Aluminium migration out of the cathode contact pad is observed with pronounced precipitations on the interconnect side walls. SEM and EDX are applied to identify sites and nature of the electromigration product.     

Capabilities of X-ray topography for studying interfacial instabilities during directional solidification

X-ray topography is very sensitive to segregation inhomogeneities. It is shown that the related contrasts can be used for revealing, over large distances, different features of the instabilities of the growth interface. Additional information can be obtained from orientation contrast. The capabilities of the method are illustrated on In doped GaAs.     

Promotion of crystal growth rate in aqueous solution by direct contact with gas corona discharge

A new technique to promote crystal growth in aqueous solution using gas plasma is proposed. In this method, short‐lived radical species produced in solution which is contacted with gas corona discharge play a role to increase chemical potential of inorganic solute. In an experimental examination, single crystal of KDP was grown in a supersaturated solution which receives oxygen ions and radicals from adjacent corona discharge in air. KDP crystal has two unique growth faces (100) and (101), and the growth rates of both faces were increased considerably by generating the corona discharge. The both growth rates with and without corona discharge were well converged by one function based on chemical potential supersaturation. This result revealed that the solution in contact with gas corona discharge has a larger capacity of chemical potential than that without the discharge. Short‐lived species induced by gas corona discharge are considered to be anti‐solvents to cause this effect. The crystal growth process proposed here is considered to be an excellent method in terms of low impurity inclusion because such short‐lived species do not remain in the final crystal products and solution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

碳纳米管负载RuO2纳米颗粒的制备及其Li-CO2电池性能

本文以水合三氯化钌溶液作为前驱体,通过简单的水热法将二氧化钌(RuO₂)纳米颗粒均匀负载在碳纳米管(CNT)基底上,成功制备出二氧化钌纳米颗粒分散均匀且具有三维多孔结构的RuO₂-CNT催化阴极。在相互交联的碳纳米管构成的三维多孔结构和RuO₂纳米颗粒高效的催化活性的双重作用下,显著提高了Li-CO₂电池的放电容量和循环性能。在100 mA·g^-1的电流密度下,首次放电比容量可达1 912 mAh·g^-1。此外,在电流密度100 mA·g^-1和恒定容量为500 mAh·g^-1的条件下,可稳定循环120个周期。本工作为Li-CO₂电池催化阴极的设计和制备提供了一种新的思路。     

Growth mechanisms of GaAs nanowires by gas source molecular beam epitaxy

GaAs nanowires were grown on GaAs (1 1 1)B substrates in a gas source molecular beam epitaxy system, using self-assembled Au particles with diameters between 20 and 800 nm as catalytic agents. The growth kinetics of the wires was investigated for substrate temperatures between 500 and 600 °C, and V/III flux ratios of 1.5 and 2.3. The broad distribution of Au particles enabled the first observation of two distinct growth regimes related to the size of the catalyst. The origins of this transition are discussed in terms of the various mass transport mechanisms that drive the wire growth. Diffusion of the growth species on the 2-D surface and up the wire sidewalls dominates for catalyst diameters smaller than ∼130 nm on average, while direct impingement on the catalyst followed by bulk diffusion through the Au particle appears to sustain the wire growth for larger catalyst diameters. A change in wire sidewall facets, indicating a probable transition in the crystal structure, is found to be primarily dependent on the V/III flux ratio.