Special features of structural defects in undoped CdTe textured ingots produced by free growth from a gasdynamic vapor flow

The structural features of undoped CdTe ingots grown in a gasdynamic flow at 620°C were studied by selective etching and X-ray diffractometry. It is found that the samples grown at a deposition rate of up to 500 μm/h consist of independently growing rods with both [111] A and [111] B directions. This indicates that the vapor composition in the growth region is almost stoichiometric. Both rod types exhibited transverse striations due to rotation twins. The twin boundaries in rods with the growth direction [111] A were shown to be also small-angle boundaries with additional misorientation of separate twins of 0.2°–0.3°. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 2, 2003, pp. 129–133. Original Russian Text Copyright ? 2003 by Klevkov, Martovitskii, Medvedev.     

Analysis of CZT crystals and detectors grown in russia and the ukraine by high-pressure bridgman methods

Sandia National Laboratories (SNL) is leading an effort to evaluate vertical high pressure Bridgman (VHPB) Cd_1−xZn_xTe (CZT) crystals grown in the former Soviet Union (FSU) (Ukraine and Russia), in order to study the parameters limiting the crystal quality and the radiation detector performance. The stoichiometry of the CZT crystals, with 0.04<x<0.25, has been determined by methods such as proton-induced x-ray emission (PIXE), x-ray diffraction (XRD), microprobe analysis and laser ablation ICP mass spectroscopy (LA-ICP/MS). Other methods such as triaxial double crystal x-ray diffraction (TADXRD), infrared transmission spectroscopy (IR), atomic force microscopy (AFM), thermoelectric emission spectroscopy (TEES) and laser induced transient charge technique (TCT) were also used to evaluate the material properties. We have measured the zinc distribution in a CZT ingot along the axial direction and also its homogeneity. The (Cd+Zn)/Te average ratio measured on the Ukraine crystals was 1.2, compared to the ratio of 0.9–1.06 on the Russian ingots. The IR transmission showed highly decorated grain boundaries with precipitates and hollow bubbles. Microprobe elemental analysis and LA-ICP/MS showed carbon precipitates in the CZT bulk and carbon deposits along grain boundaries. The higher concentration of impurities and the imperfect crystallinity lead to shorter electron and hole lifetimes in the range of 0.5–2 and 0.1 μs, respectively, compared to 3–20 and 1–7 μs measured on U.S. spectrometer grade CZT detectors. These results are consistent with the lower resistivity and worse crystalline perfection of these crystals, compared to U.S.-grown CZT. However, recently grown CZT from FSU exhibited better detector performance and good response to alpha particles.     

In掺杂CdMnTe晶体的Te气氛退火研究

Thermal annealing in Te vapor atmosphere was adopted to improve the properties of indium-doped Cd_1-xMn_xTe（x=0.2,CdMnTe） wafers grown by the vertical Bridgman method.The wafers before and after annealing were characterized by measuring the Te inclusions,etch pit density（EPD）,Mn composition,resistivity, and impurity.IR transmission microscopy and EPD measurements revealed that the densities of Te inclusions reduced from（5-9）×10⁴ cm^-3 to（2-4）×10⁴ cm^-3 and EPD from 10⁵ cm^-2 to 10⁴ cm^-2 after annealing. NIR transmission spectroscopy showed that the Mn composition increased by 0.002-0.005 mole fractions during the annealing.The resistivity of the wafers improved from（2.0-4.5）×10⁸Ω·cm to（1.7-3.8）×10⁹Ω·cm,which suggested that the deep-level donor of Te antisites was successfully introduced after annealing.Inductively coupled plasma-mass spectrometry（ICP-MS） revealed that the concentrations of impurities in the wafer decreased,which indicated the purifying effects of Te vapor annealing on the wafers.All the results demonstrate that the Te vapor annealing of the indium-doped CdMnTe crystal has positive effects on the crystallinity,resistivity and purity of CdMnTe wafers.     

Optical absorption properties of HgCdTe epilayers with uniform composition

Hg_1−xCd_xTe is an important material for high-performance infrared detection for a wide spectral range, from 1.7 μm to beyond 14 μm. An accurate understanding of the relationship between optical absorption and bandgap energy of this semiconductor alloy is needed for pre-process layer screening, detector design, and interpretation of detector performance. There is currently a disparity among the infrared detector community in relating the optical absorption properties to HgCdTe alloy composition and bandgap energy. This disagreement may stem from a misunderstanding of absorption properties, where existing models were developed decades ago using either bulk material or material with nonuniform composition. In this work, we have initiated an investigation of the optical absorption properties of HgCdTe with uniform composition grown by molecular-beam epitaxy (MBE) with in-situ compositional control via spectroscopic ellipsometry. The absorption properties show unique characteristics in the bandtail region, with insignificant temperature dependence. The absorption properties above the bandgap suggest a hyperbolic bandstructure as opposed to the common assumption of a parabolic bandstructure. The temperature dependence of the bandgap energy shows good agreement to the commonly used expression developed previously by Hansen et al.     

Investigation into the InAs/GaAs quantum dot material epitaxially grown on silicon for O band lasers

InAs/GaAs quantum dot(QD)lasers were grown on silicon substrates using a thin Ge buffer and three-step growth method in the molecular beam epitaxy(MBE)system.In addition,strained superlattices were used to prevent threading disloca-tions from propagating to the active region of the laser.The as-grown material quality was characterized by the transmission electron microscope,scanning electron microscope,X-ray diffraction,atomic force microscope,and photoluminescence spectro-scopy.The results show that a high-quality GaAs buffer with few dislocations was obtained by the growth scheme we de-veloped.A broad-area edge-emitting laser was also fabricated.The O-band laser exhibited a threshold current density of 540 A/cm² at room temperature under continuous wave conditions.This work demonstrates the potential of large-scale and low-cost manufacturing of the O-band InAs/GaAs quantum dot lasers on silicon substrates.     

Analysis of copper grains in damascene trenches after rapid thermal processing or furnace anneals

The microstructures of Cu lines in damascene trenches annealed at temperatures from room temperature to 425°C using both rapid thermal processing (RTP) and furnace annealing were investigated using an array of characterization techniques including transmission electron microscopy (TEM), focused ion beam, scanning electron microscopy (SEM), and electron backscatter diffraction-orientation-imaging microscopy (EBSD-OIM). It was found that the final grain sizes strongly depend on the annealing process used; RTP generated larger grains than furnace annealing. The Cu line electrical resistance correlated with grain size differences observed for RTP and furnace anneals. The ramping rate, not the annealing time, played the critical role in the grain growth process. In either case, a high density of Σ3 coincident site lattice (CSL) twin boundaries was observed in the Cu lines. Forty-five percent of the grain boundaries measured were found to be Σ3 CSL twins, which are differentiated from random high-angle boundaries by having preferred electrical and diffusion properties. The minimum feature dimension of width or height of the damascene trenches limited the average grain size. Prior to the trench height limitation, the average grain size increased linearly with the trench width. The Cu (111) texture became stronger as the trench width increased up to 0.5 μm; for wider trenches, the texture did not increase further.     

Amorphous and nanophase microstructures of bulk Se-based chalcogenide alloys

The composition-dependent microstructural morphology variations of Se89Zn2Te5In4 and Se87Zn2Te5In6 chalcogenide alloys are investigated. Glassy and nanophase surfaces and structural morphologies of these alloys have been described with help of scanning electron microscope (SEM) and transmission electron microscope (TEM), and their elemental concentrations are confirmed from the energy dispersive X-ray spectroscopy (EDX). Experimental results demonstrate that the microstructure of Se89Zn2Te5In4 alloy belongs to pure glassy state, while the Se87Zn2Te5In6 alloy is with nanophase structure.     

A different approach for determining the responsivity of n+p detectors using scanning electron microscopy

There is an ever growing need for highly effective electron detectors with high responsivity which is usually a function of the wavelength of the incident radiation and of the properties of the sensor used. One of the parameters that has been shown to have a negative influence on the responsivity of a radiation detector is the surface recombination velocities of minority carriers at the Si-SiO2 interface. Usually, MOS capacitors/transistors and gated diodes are employed to study the properties of the silicon detector surface. The main motivation for this work is to explore an alternative to standard to study the responsivities (the input–output gain) and other detector behaviours at low electron energy. Though the research is not aimed at comparing and contrasting the results of the differently doped n p detectors, its purpose is to provide an alternative characterization method (using scanning electron microscopy) to other methods used in previous studies on the responsivity of n p doped detectors as a function of the electron radiation energy and other interface parameters.     

Blue light emission from pulsed laser ablated polyethylene

The 1064 nm pulsed laser was used to ablate polyethylene （PE） at different power. Compared with unmodified PE, the ablated polyethylene （PE） gave off obvious blue light under UV lamp irradiation. The morphology and tre structure of ablated and unmodified PE were studied by scanning electron microscope, fluorescence spectroscopy and raman spectroscopy. the results showed that double bonds existed in the ablated PE which resulted in obvious blue emission of ablated PE and the intensity of the laser had great influence on the physical properties and chemical structure of the PE surface.     

Ti-6A1-4V表面激光熔覆钛基复合涂层的微观组织及形成机制

Titanium matrix composite coatings were fabricated on Ti-6A1-4V substrate by laser cladding using powder mixtures of Ti Cr3C2 and Ti TiB2, respectively. The chemical compositions and mi-crostructures of the coatings were analyzed using scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). Microhardness was measured by a microhardness tester. The results showed that Cr3C2 particles were dissolved and deposited to form dendritic TiC in the upper section and spherical grain TiC in the bottom of Cr3C2 Ti coating. Most of TiB2 was dissolved in the molten pool by laser irradiation, then formed TiB with fine needles and coarse needles in the TiB2 Ti coating. A few quasi-melted TiB2 particles with irregular shape at the bottom of the coating were observed. The average microhardnesses were approximately HV850-V1000, HV800-V1050 in the Cr3C2 Ti and TiB2 Ti coating, respectively, which were 2-3 times higher than that of Ti-6A1-4V substrate.     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.