Cz-Silicon Produced from Solar Grade and Recycled Materials. Part I: Bulk Properties and Formation of As-Grown Defects

Abstract

The current paper is the first of two, investigating the properties of Czochralski-silicon (Cz-silicon) materials and solar cells produced with recycled and compensated silicon materials. In this work, impurity levels in two experimental Cz-silicon ingots were characterized by glow discharge mass spectroscopy and FTIR. The combined effects of these impurities on recombination properties were investigated by photoluminescence imaging and compared to bulk properties of a reference ingot. Ring pattern distribution of as-grown micro-defects in the ingots, related to elevated carbon and oxygen levels, were delineated based on the results of two steps of dry oxidation. Moreover, the mechanism of defect formation in the experimental Cz-Si during solidification and oxidation is elaborated in light of thermodynamic theories. Meanwhile, the positive effect of phosphorus in compensated feedstock is discussed in relation to the minority carrier lifetime based on the quasi-steady-state photoconductance results, as well as on the restricted formation of oxygen-related defects during solidification by analyzing samples after oxidation and copper decoration.