Interaction between process technology and material quality during the processing of multicrystalline silicon solar cells

Multicrystalline silicon is the most used material for the production of silicon solar cells. The quality of the as grown material depends on the quality of the feedstock and the crystallization process. Bulk impurities, crystal defects like dislocations and of course the grain boundaries determine the material quality and thus the solar cell conversion efficiency. Therefore minority carrier lifetime measurements are often done to characterize the material quality. But the measured values are from limited use because it is known that the solar cell process itself can dramatically change the minority carrier lifetime and the solar cell efficiency. In order to obtain more detailed information of the behaviour of different defect types additionally high-resolution LBIC (light beam induced current)-measurements have been done. Since LBIC needs a pn-junction for photocurrent generation the LBIC technique has been combined with the a-Si/c-Si heterojunction cell process, which makes it possible to manufacture solar cells even from as cut wafers without changing the material quality. With this combination of measurement and preparation techniques it was possible to analyze the influence of the diffusion process and the firing process on the behaviour of the three different defect types: grain boundaries, dislocation networks and bulk impurities.     

Static fatigue lifetime of optical fibers assessed using Boltzmann–Arrhenius–Zhurkov (BAZ) model

The recently suggested probabilistic design-for-reliability (PDfR) concept and particularly its physically meaningful and flexible Boltzmann–Arrhenius–Zhurkov (BAZ) model, can be effectively employed as an attractive replacement of the widely used today purely empirical and physically unsubstantiated power law relationship for assessing the static fatigue (delayed fracture) lifetime of optical silica fibers. In this analysis the BAZ model is employed to estimate the static fatigue lifetime of an optical silica fiber under the combined action of tensile loading and an elevated temperature. The PDfR concept has its experimental basis in the highly-focused and highly-cost-effective failure-oriented accelerated testing (FOAT). Accordingly, it is shown how the PDfR concept, BAZ model and FOAT data can be effectively used, when there is a need to assess the long-term tensile strength (static fatigue life) of a coated optical fiber subjected to the combined action of tensile loading and elevated temperature. Although the role of elevated humidity might be insignificant owing to the elevated temperature conditions, this role can be accounted for, if there is a need for that, as well, by using multi-parametric BAZ model. Since the principle of superposition does not work in reliability engineering, all the three stressors, namely, the elevated temperature, tensile stress and relative humidity, should be applied concurrently to the specimen under test, and their coupling, if any, should and could be considered by the FOAT based on the BAZ model. The numerical example is carried out, however, for the case when only the elevated temperature and tensile stress are applied. The results of the analysis can be employed in the design and testing of optical silica fibers.     

Electron drift velocity measurements in liquid krypton–methane mixtures

Electron drift velocities have been measured in liquid krypton, pure and mixed with methane at different concentrations (1–10% in volume) versus electric field strength, and a possible effect of methane on electron lifetime has been investigated. While no effect on lifetime could be detected, since lifetimes were in all cases longer than what measurable, a very large increase in drift velocity (up to a factor 6) has been measured.     

Molecular pore size characterization within chitosan biopolymer using positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy has been used to study a chitosan biopolymer, to which nanoclay has been added, and the effect of water absorption and cross-linking on the microporosity. All measurements were conducted at room temperature. The free volume size of the biopolymer samples was obtained based on the ortho-positronium lifetime, and the relative concentration of free volume cavities was measured by the ortho-positronium intensity. Using the PALS technique, effects of hydration were observed as a reduction in the measured pore size. Similarly, the cross-linked samples exhibited an increase in intensity of the smallest pores commensurate with the SEM observations.     

Referencing techniques for the analog mean-delay method in fluorescence lifetime imaging

The analog mean-delay (AMD) method is a new powerful alternative method in determining the lifetime of a fluorescence molecule for high-speed confocal fluorescence lifetime imaging microscopy. Even though the photon economy and the lifetime precision of the AMD method are proven to be as good as those of the state-of-the-art time-correlated single photon counting method, there have been some speculations and concerns about the accuracy of this method with respect to the absolute lifetime value of a fluorescence probe. In the AMD method, the temporal waveform of an emitted fluorescence signal is directly recorded with a slow digitizer whose bandwidth is much lower than the temporal resolution of the lifetime to be measured. We have found that the drifts and the fluctuations of the absolute zero position in a measured temporal waveform are the major problems in the AMD method. We have proposed electrical and optical referencing techniques that may suppress these errors. It is shown that there may exist more than 2 ns drift in a measured temporal waveform during the period of the first 12 min after electronic components are turned on. The standard deviation of a measured lifetime after this warm-up period can be as large as 51 ps without any referencing technique. We have shown that this error can be reduced to 9 ps with our electronic referencing technique. It is demonstrated that this can be further reduced to 4 ps by the optical referencing technique we have introduced.     

Simulation of deformation and lifetime behavior of a fcc single crystal superalloy at high temperature under low-cycle fatigue loading

This work deals with the formulation of a three-dimensional crystallographic time-incremental lifetime rule for face-centered cubic (fcc) single crystals used for gas-turbine blade applications. The damage contribution rate of each slip system to the total damage is governed by the current values of the resolved shear stress and the slip rate on the corresponding slip system. The damage rule is combined with a crystallographic viscoplastic deformation model. For the nickel-base single-crystal superalloy CMSX4 at 950 °C, various strain- and stress-controlled uniaxial cyclic tests with and without hold-times can be described for different crystal orientations by one set of material parameters. For verification, simulation results for a single-crystal specimen with a notch have been compared with corresponding experimental results. The predicted lifetime is within the factor of two of the measured one.     

Integrated instrumentation amplifier for the phase readout ofpiezoresistive strain gauges

An integrated instrumentation amplifier combined with a bandpass filter has been fabricated in a bipolar process for the phase readout of piezoresistive sensors. Changes in the resistance can be measured directly using an ac-operated bridge configuration. A special technique has been employed to convert these changes into a phase angle relative to the excitation signal. The instrumentation amplifier should have a very high Common-Mode Rejection Ratio (CMRR) at a relatively high bridge operating frequency (100 kHz) in order to actually exploit the advantages of this readout method. The filter should have a well-determined phase behavior to prevent a change in the frequency from affecting the output phase angle. Special emphasis has been placed on the compatibility between micromachining technologies in silicon and bipolar processing, so that a fully integrated smart silicon micromechanical sensor can be made     

Imaging of fluorescent yield and lifetime from multiply scattered light reemitted from random media

The feasibility of employing fluorescent contrast agents to perform optical imaging in tissues and other scattering media has been examined through computational studies. Fluorescence lifetime and yield can give crucial information about local metabolite concentrations or environmental conditions within tissues. This information can be employed toward disease detection, diagnosis, and treatment if noninvasively quantitated from reemitted optical signals. However, the problem of inverse image reconstruction of fluorescence yield and lifetime is complicated because of the highly scattering nature of the tissue. Here a light propagation model employing the diffusion equation is used to account for the scattering of both the excitation and fluorescent light. Simulated measurements of frequency-domain parameters of fluorescent modulated ac amplitude and phase lag are used as inputs to an inverse image-reconstruction algorithm, which employs the diffusion model to predict frequency-domain measurements resulting from a modulated input at the phantom periphery. In the inverse image-reconstruction algorithm, a Newton-Raphson technique combined with a Marquardt algorithm is employed to converge on the fluorescent properties within the medium. The successful reconstruction of both the fluorescence yield and lifetime in the case of a heterogeneous fluorophore distribution within a scattering medium has been demonstrated without a priori information or without the necessity of obtaining absence images.     

Positron Lifetime Study of the Single-Phase B2 Ni100-xAlx and Ni50-xCoxAl50 Intermetallics

To whom correspondence should be addressedE-mail: jtguo@imr.ac.cn1. IntroductionIt is now well established that the mechanicalproperties of NIAI are strong functions of composition and often of thermal history. These dependencieshave been correlated in part to the presence of pointdefects. The observation of off-stoichiometric hardening in NiAI, for instance, has been attributed tothe constitutional point defects[1'2]. Previous investigators have attempted to relate this hardening tothe co…     

In vitro real-time characterization of cell attachment and spreading

A method based on the piezoelectric quartz crystal microbalance (QCM) technique for in vitro real-time characterization of cell attachment and spreading on surfaces has been developed. The method simultaneously measures the resonant frequency, f, and the dissipation energy, D, of the oscillating system. The QCM responses are sensitive to very small amounts (a few hundreds) of cells and highly specific to surface chemical properties. The first results from deposition of cells on two polystyrene surfaces of different wettability in serum-containing medium are reported. It has previously been shown that a decrease in f is related to the degree of cell spreading. In our data it appears that the extent or quality of cell attachment is reflected in an increase in D caused by adhering cells. The combined information from f and D measured by this technique might therefore be useful to probe cell–surface interactions for biomaterials. © 1998 Kluwer Academic Publishers     

An in situ glow discharge cleaning method for the LEP vacuum system

The performance of the vacuum systems of present day electron storage rings is limited by synchrotron radiation induced gas desorption. A method to reduce the electron induced desorption yield (thought to be a measure of the radiation induced desorption) by glow discharge cleaning has been developed. Initial beam lifetimes for standard LEP operation (Large Electron Position Storage Ring) have been calculated based on measured electron stimulated desorption yields and two different proposed pumping systems. (One with distributed ion pumps, the other with distributed getter pumps). After bakeout, both systems would provide an initial beam lifetime of ～ 4 min. After a helium glow discharge for 3 h at 150°C (at 1.5 torr and with a discharge current of 0.7 A m^?1), a lifetime of ～6.7 h would be obtained in the ion pumped system as compared to ～1.7 h in the getter pumped version. Results obtained with Argon discharge proved to be inferior.     

Fluorescence from airborne microparticles: dependence on size, concentration of fluorophores, and illumination intensity

We measured fluorescence from spherical water droplets containing tryptophan and from aggregates of bacterial cells and compared these measurements with calculations of fluorescence of dielectric spheres. The measured dependence of fluorescence on size, from both droplets and dry-particle aggregates of bacteria, is proportional to the absorption cross section calculated for homogeneous spheres containing the appropriate percentage of tryptophan. However, as the tryptophan concentration of the water droplets is increased, the measured fluorescence from droplets increases less than predicted, probably because of concentration quenching. We model the dependence of the fluorescence on input intensity by assuming that the average time between fluorescence emission events is the sum of the fluorescence lifetime and the excitation lifetime (the average time it takes for an illuminated molecule to be excited), which we calculated assuming that the intensity inside the particle is uniform. Even though the intensity inside the particles spatially varies, this assumption of uniform intensity still leads to results consistent with the measured intensity dependence.     

半导体材料少子寿命测试仪的研制开发

少数载流子寿命(简称少子寿命)是半导体材料的一项重要参数，它对半导体器件的性能、太阳能电池的效率都有重要的影响。我们采用微波反射光电导衰减法研制了一台半导体材料少子寿命测试仪，本文将对测试仪的实验装置、测试原理及程序计算进行了较详细的介绍，并与国外同类产品的测试进行比较，结果表明本测试仪测试结果准确、重复性高，适合少子寿命的实验室研究和工业在线测试。     

Minority carrier diffusion length in undoped p-type epitaxially grown CdxHg1-xTe

High minority carrier lifetimes in diffusion limited p-n photodiodes result in low dark currents and a high R₀A figure of merit. Minority carrier diffusion length should be an important indicator of device performance through its link with the minority carrier lifetime. The diffusion length can be measured directly on a p-n junction device using electron beam induced current (EBIC) measurements. This paper compares diffusion lengths in epitaxially grown Cd_xHg_1-xTe measured directly using EBIC, with those predicted from both transient and steady state lifetime measurements using Einstein's relation. In all cases, as-grown layers are vacancy-doped p-type.     

Improvement of beam lifetime and vacuum system of the PF-AR

Successive improvements have been performed on the vacuum system for the Photon Factory Advanced Ring (PF-AR) at the High Energy Accelerator Research Organization (KEK). The main purpose is to prolong electron beam lifetime for stable operation as an intense pulsed X-ray source. In the past three years, a total of 61 sputter ion pumps (SIPs) were additionally installed, and the increased effective pumping speed amounts to 13% of total. Comparison between calculated and observed beam lifetimes indicates that the lifetime is restricted mainly by the residual gas scatterings and that improvement of the vacuum will realize still longer lifetime. Sudden beam lifetime drops caused by dust trappings have been investigated for many years. The frequency of the lifetime drops has decreased as operation time elapsed after a large-scale reconstruction. Effect of distributed ion pumps (DIPs) on the lifetime drops has also been investigated experimentally.     

Luminescence Lifetime–Based In Vivo Detection with Responsive Rare Earth–Dye Nanocomposite

For years, luminescence lifetime imaging has served as a quantitative tool in indicating intracellular components and activities. However, very few studies involve the in vivo study of animals, especially in vivo stimuli‐responsive activities of animals, as both excitation and emission wavelengths should fall into the near‐infrared (NIR) optical transparent window (660–950 and 1000–1500 nm). Herein, this work reports a lifetime‐responsive nanocomposite with both excitation and emission in the NIR I window (800 nm) and lifetime in the microsecond region. The incorporation of Tm³⁺‐doped rare‐earth nanocrystals and NIR dye builds an efficient energy transfer pathway that enables a tunable luminescence lifetime range. The NaYF₄:Tm nanocrystal, which absorbs and emits photons at the same energy level, is found to be 33 times brighter than optimized core–shell upconversion nanocrystals, and proved to be an effective donor for NIR luminescence resonance energy transfer (LRET). The anti‐interference capability of luminescence lifetime signals is further confirmed by luminescence and lifetime imaging. In vivo studies also verify the lifetime response upon stimulation generated in an arthritis mouse model. This work introduces an intriguing tool for luminescence lifetime–based sensing in the microsecond region.     

Estimation of exponential component reliability from uncertain life data in series and parallel systems

Estimating reliability of components in series and parallel systems from masking system testing data has been studied. In this paper we take into account a second type of uncertainty: censored lifetime, when system components have constant failure rates. To efficiently estimate failure rates of system components in presence of combined uncertainty, we propose a useful concept for components: equivalent failure and equivalent lifetime. For a component in a system with known status and lifetime, its equivalent failure is defined as its conditional failure probability and its equivalent lifetime is its expectation of lifetime. For various uncertainty scenarios, we derive equivalent failures and test times for individual components in both series and parallel systems. An efficient EM algorithm is formulated to estimate component failure rates. Two numerical examples are presented to illustrate the application of the algorithm.     

Spectroscopic analysis and the effects of color centers on the laser performance of Nd: CaZn2Y2Ge3O12

Spectroscopic and EPR investigations of Nd³⁺-doped CaZn₂Y₂Ge₃O₁₂ (CAZGAR) have been performed. The absorption, fluorescence, excitation spectra and fluorescence lifetime have been measured at room temperature. The Judd-Ofelt theory has been applied to the measured optical absorption intensities to predict the radiative decay rates, branching ratios, and peak stimulated emission cross section from the metastable ⁴F_3/2 state to the ⁴I_9/2 manifold. The fluorescence lifetime of the ⁴F_3/2 level of Nd³⁺ at low concentration in this host was measured to be 285 ± 10 μs, which is longer than that for Nd³⁺: YAG. Color centers located at zinc octahedral sites have been produced in these crystals by ultraviolet irradiation and have been detected by EPR techniques. The effects of the color centers on the potential laser characteristics of this materials are discussed.     

Experiments and stochastic model for propagation lifetime of railway axles

Inspection intervals of critical safety components should be calculated on the basis of sophisticated crack growth algorithms able to describe crack propagation under service loads. The present paper deals with a probabilistic application of the NASGRO crack growth algorithm to estimate the propagation lifetime of railway axles. The analysis of experimental crack growth and threshold data of an A1N steel has enabled us to propose two random variable models for the estimation of propagation lifetimes, discussing their statistical properties and their implications for lifetime estimates.     

Fast,high resolution,inline contactless electrical semiconductor characterization for photovoltaic applications by microwave detected photoconductivity

The state-of-the art lifetime measurement technique MDP (microwave detected photoconductivity) is presented with its latest developments in sensitivity, measurement speed and data simulation. Several applications and examples in the field of inline material characterization, defect recognition and real time statistical process control in silicon bricks and wafers are presented, demonstrating the practical use of MDP measurements and of the data obtained by it. The measured lifetime itself combined with its spatial distribution and the measured steady state photoconductivity enable a good correlation to the cell efficiency. Furthermore, the paper presents a detailed summary of the properties of steady state and non-steady state microwave based minority carrier lifetime measurement techniques to complete this extensive study.