Methods to Improve Bulk Lifetime in n-Type Czochralski-Grown Upgraded Metallurgical-Grade Silicon Wafers

This paper investigates the potential of three different methods— tabula rasa (TR), phosphorus diffusion gettering (PDG), and hydrogenation, for improving the carrier lifetime in n-type Czochralski-grown upgraded metallurgical-grade (UMG) silicon samples. Our results show that the lifetimes in the UMG wafers used in this study were affected by both mobile metallic impurities and as-grown oxygen precipitate nuclei. Thus, the dissolution of grown-in oxygen precipitate nuclei via TR and the removal of mobile impurities via PDG step were found to significantly improve the electronic quality of the UMG wafers. Finally, we report bulk lifetimes and 1-sun implied open-circuit voltages of the UMG wafers after boron and phosphorus diffusions, as typically applied in n-type cell fabrication.