GROWTH AND CHARACTERIZATION OF POLYCRYSTALLINE SILICON INGOTS FROM METALLURGICAL GRADE SOURCE MATERIAL

Silicon crystals are grown from 98% pure metallurgical-grade source material by the Czochralski technique in an attempt to apply them to solar cells. Their crystallinity, impurity content and electrical properties are investigated. Inclusions, observed in the crystals grown at higher rates than 1 mm/min, or when the solidified fraction is over 0.4, are identified as Si-A1 alloys by electron probe micro-analysis. The impurity concentration in the crystals depends mainly on the growth rate. The growth rate of 0.5 mm/min is found to be the optimum for preparing relatively pure crystals. The impurity concentration cannot be decreased to the level expected from the segregation coefficient. This reason is considered to be due to the existence of small-sized inclusions and the formation of cellular structure. © 1979.