Phosphorus diffusions for gettering-induced improvement of lifetime in various silicon materials

摘要

Solar-grade silicon frequently contains large quantities of defects and impurities that can significantly degrade the excess-carrier lifetime through introduction of recombination sites. The impurities frequently include metals as well as high concentrations of high carbon and/or oxygen. Defects and impurities can also degrade the electrical properties of solar cells fabricated in solar-grade silicon by causing shunt currents or excess junction current. Fabrication of acceptable solar cells from such materials requires processes that are tolerant of, or that can even improve impure and defective material. Phosphorus diffusion is a well-known technique for gettering of impurities in silicon. The effect of phosphorus diffusion on the excess-carrier lifetime in various silicon materials was investigated. The optimum phosphorus diffusion schedule and enhancement of lifetime was found to be material specific, with substantial (5-fold) increases found for some materials. Possible reasons for the variability of phosphorus gettering with different materials is discussed. 11 refs., 6 figs., 3 tabs.