Block specimens of Ca(PO,), glass crystallize easily at temperatures considerably lower than the glass transition temperature, T,; thin blown films of the glass do not exhibit this behavior. The crystals, which are P-Ca(PO,), with a trace of the y form, are identical to those formed above T,; they exhibit "hemispherulitic" growth from the glass surface. The activation energy for crystal growth below T, is 30 kcal/mol, which indicates that the growth mechanism differs from that in blown film samples above T,, (activation energy = 110 kcal/mol). A model for crys-terms of induced tension in the molecular chains at the glasscrystal interface.
The origins of metal impurities in Czochralski-grown single-crystal silicon were investigated in order to develop crystals with improved radial impurity homogeneity. The radial metallic impurity distribution in silicon crystals was evaluated by means of minority carrier recombination lifetime. The crystal circumference was found to be an area of degraded lifetime. A quantitative analysis of radial impurity distribution in silicon was carried out using deep level transient spectroscopy techniques. Iron was the predominant impurity detected on the circumference of the crystal. The radial distribution of iron impurity concentration showed good correlation with calculated results. An experimental technique was developed which allowed us to isolate the influence of the graphite parts of the Czochralski furnace as a contamination source during high-temperature processing. Commercially available graphite materials of different purity levels, both with and without silicon carbide coatings, were evaluated. It was confirmed that the graphite furnace parts play a role in determining the radial impurity distribution profile.
InfroductionHeavy metals strongly influence the electrical characteristics of silicon devices. The initial electrical effect is the introduction of energy levels near the center of the
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.