  Upgraded metallurgical-grade (UMG) Si is obtained via a purification route
alternative to the one used for conventional polysilicon and with significantly
reduced environmental impact. Additionally, despite a lower purity level in the
feedstock than polysilicon, UMG-Si has demonstrated potential for the
fabrication of highly efficient and low-cost solar cells. Low initial bulk
carrier lifetimes recorded in UMG-Si bare wafers can be improved by means of an
adequate Phosphorus Diffusion Gettering (PDG) process to the level of mc-Si. In
this letter, optimized PDG processes for UMG-Si are reported, resulting in
increased values between 20 and 250 times the original carrier lifetimes and
record figures above 645 us.
