The monocrystalline PV-FZ/sup /spl trade// float zone silicon product is presented with emphasis on the bulk characteristics of the product. It is demonstrated that the effective bulk lifetime can be guaranteed in all points including the periphery of the PV-FZ/sup /spl trade// ingot. A back contacted thin film solar cell design is presented and a processing roadmap for high efficiency solar cells is described.

When solar cells are manufactured by use of float zone (FZ) grown monocrystalline silicon, it is possible to achieve efficiencies near 25%. This value is significantly higher than the typical efficiency of commercial cells (13-16.5%) that is manufactured on Czochralski (CZ) grown monocrystalline or casted polycrystalline silicon. The electronic grade FZ growth process however, requires an expensive form of silicon feedstock material that brings the price of a FZ wafer far above the acceptable range for the PV industry. In order to overcome this dilemma, Topsil has developed a new crystal puller and a new set of process recipes that can accept a larger and rougher type of low cost feedstock. Hereby it is possible to manufacture FZ silicon wafers at the same cost as CZ wafers, without reducing the quality and compromising the efficiency potential of the FZ material.

The interface structure of bonded Si(001) wafers with twist angle 6.5 ° is studied as a function of annealing temperature. An ordered structure is observed in x-ray diffraction by monitoring a satellite reflection due to the periodic modulation near the interface, which results from the formation of a regular array of screw dislocations. This satellite reflection first appears at an annealing temperature of 800 °C, and increases abruptly up to temperatures of 1000 °C. We propose that this transition occurs when there is sufficient mobility for the reorganization of atomic steps and terraces in the interface region.

A proper theoretical and experimental analysis of the electrical response (measurement of the complex electrical impedance (Z) over tilde(omega)) in higher resistivity materials at classical frequencies below 1 GHz has revealed a number of important and interesting results [1]. The EIS experimental method and the subsequent analysis yield, in principle, a whole range of electrical material parameters without usual limitations caused by possible high resistivities of the studied material and/or by nature of electrical contacts. In cases where other methods are applicable, the determination of these parameters would require a whole number of them (examples are 4DCPR, Hall effect, quasi-static C-V, DLTS and others). Some illustrative results obtained from EIS measurements and analysis on pure, single crystal silicon (bath n- and p-type variety) are presented.

Fusion-bonded silicon wafers exhibit a superstructure at their common interface due to the spatial beating of the two crystal lattices. The superstructure consists of a network of screw dislocations with a period determined by the twist angle θ. By synchrotron X-ray diffraction, the periodic elastic modulation in the two crystals resulting from the dislocation network has been measured. The characteristic thickness of the modulated region is found to be inversely proportional to θ, reaching over 160 Å for θ=0.4°. This behavior is reproduced in numerical simulations of the elastic modulation.

Neutron Transmutation Doping (NTD) of silicon has been in use for 25 years. The process is based on irradiation of Si with neutrons. The process was originally developed by Topsil, and has been the major building stone for power devices since the seventies. The process has been studied intensively in the past. Here we will give a resume of the major aspects of the technique, the applications and finally take a look into the future, where we will see applications for even higher voltage and higher power. This evolution is driven by two parallel technological progresses. On one hand, the resistivity of the silicon crystal prior to irradiation is increasing, and on the other hand, the resistivity tolerances of the material with resistivities below 100 Omega cm prepared by the conventional gas phase doping technique, are decreasing.

Bonded silicon wafers of high resistivity have been characterized with respect to interface static charge density, interface barrier and interface recombination activity by use of Spreading Resistance Probe, Electrical Impedance Spectroscopy, static I-V, and Photo Conductive Decay techniques.Different cleaning recipes have been applied, and the HF-cleaning treatment has shown to posses the best electrical properties, due to the formation of Si/Si bonds, in contrast to the other samples, where an oxide layer is encapsulated between the true wafers.

Electrical impedance spectroscopy (EIS), where the complex frequency dependent electrical impedance of a semiconductor sample is measured as function of temperature and de-bias voltage, is a general and very versatile characterisation tool. The amount of information available is quite large, as both the bulk material, the space charge region near the contacts, and the presence of deep level impurities within the space charge region, will affect the measurements. In this paper it will be shown, how this kind of measurements can be used in order to obtain the bulk conductivity, the amount of band bending of a Schottky barrier, and information on the character of contamination induced deep levels in the sample.

Electron capture detection (ECD), low- and highresolution mass spectrometry (LR- and HRMS), and atomic emission detection (AED) were compared for the gas chromatographic (GC) detection of polychlorinated biphenyls (PCBs) present in highly contaminated marine sediments. With ECD, LRMS, and even HRMS, detection was seriously disturbed by the complex matrix of the sediments, whereas AED in the chlorine-selective mode provided excellent PCB profiles without interferences. In addition, GC-AED provided congener independent responses, which enabled accurate quantitation of all PCBs based on a single calibration curve. However, because GC-AED was less sensitive than the other techniques studied, preparation of relatively large amounts of sample (10–20 g dry sediment) was required for most analyses.

Capillary gas chromatography (GC) combined with mass spectrometry (MS) and atomic emission spectroscopy (AED) was utilized for a comprehensive investigation of organic micropollutants in a marine sediment. Most compounds were found and identified by GC-MS library search. The elemental information from GC-AED was utilized for confirmation purposes, for analyte characterization in cases where identification by GC-MS was impossible, and for screening on heteroatomic components. In addition, GC-AED was effectively used for the quantitative part, where the total amount of GC amenable material, classes of compounds, and individual components were determined.

The contact wave velocity in silicon wafer bonding is experimentally found to decrease with wafer thickness and to be only weakly dependent on wafer diameter. Wafers of different thicknesses ranging from 270 to 5000 μm, were dipped in HF:H2O before bonding to give the surfaces hydrophobic properties. A model based on energy conservation can explain the main characteristics of the experimental results. The contact wave velocity is determined by the amount of energy available as kinetic energy for the entrapped gas in the gap between the wafers. By increasing wafer thickness, the elastic energy stored in the material is increased, and the contact wave velocity is decreased.

Recently developed full, dynamical analysis of the electrical response in semiconductors and insulators at classical frequencies makes it possible to use electrical impedance spectroscopy also in the investigations of electron surface states. The results will be presented for single crystal silicon with some experimental evidence that silicon surface states form Anderson negative U centers.

Three chlorinated dimethyl sulfones and five chlorinated thiophenes have been identified in the alkaline extraction liquor from a bleach plant by gas chromatography with atomic emission detection (GC-AED) and with mass spectrometry (GC-MS). The information on elemental content obtained by GC-AED enabled a rapid screening of the sulfur compounds and provided important structural information complementary to the mass spectral data. Quantitation was accomplished by GC-AED based on universal calibration.

Atomic emission spectroscopy coupled with capillary gas chromatography (GC) has been evaluated for molecular formula determination of several chlorinated and brominated compounds present in three environmental samples. Variations in elemental responses due to compound type, poor chromatographic resolution, and small signals relative to the background were all found to complicate molecular formula calculations. About 20% of the calculated molecular formulas presented in this paper agreed with theoretical values. For most applications, identifications based solely on GC coupled with atomic emission detection (AED) are not sufficiently accurate. However, the combination of elemental information derived from a GC-AED analysis with complementary data obtained from other detection techniques results in a strong analytical tool for analyte identification.

Within Levine's extension of the Phillips model the values of the homopolar, heteropolar, and average gaps were calculated for As0.5Te0.5−xSex glasses. Using the simplest version of the Penn model these values were correlated with experimentally determined values of the static dielectric constant (ϵ0exp). The agreement between calculated and experimental ϵ values has been found very satisfactory.

An effective way to achieve cost reduction in PV is to increase solar cell efficiency, which increases the module power density and reduces the balance of systems costs through lower area requirements, lower structure costs, reduced module interconnection and less installation time. This paper reports on efforts taken to develop cost-effective monocrystalline silicon substrate materials that do not suffer light induced degradation, and to use these wafers to apply laboratory concepts to industrial production to fabricate high efficiency monocrystalline solar cells. Both Ga-doped Cz ingots and PV-FZ ones have been successfully produced in a wide range of resistivities, and their high quality and lack of light induced degradation confirmed. For a laboratory process, 20.6% efficiency has been achieved on the FZ material, and 19.7% on the Ga-doped Cz. The potential of these materials to produce industrial high efficiency solar cells is shown by pilot line production of Laser Grooved Buried Contact cells of 19.2% on FZ samples and of 18.4% on Ga-doped Cz ones.