Influence of Fe Contamination on the Minority Carrier Lifetime of Multi-crystalline Silicon

We investigate the influence of Fe contamination on the minority carrier lifetimes of multi-crystalline silicon. The minority carrier lifetime is measured by the microwave photoconductive decay method. The original bulk lifetime is about 30 μs after passivation with iodine solution. After intentional Fe contamination, the bulk lifetime declines with increasing temperature. Fast cooling in air conduces to the formation of more interstitial Fe (Fe_i). Slow cooling through the control of the furnace temperature limits the formation of more Fe_i, but leads to the formation of precipitation. The data support the idea that the minority carrier lifetime in multi-crystalline silicon mainly depends on the distribution of Fe but not the total amount. A favorite effect of Fe_i gettering is discovered after conventional phosphorus diffusion, and the Fe_i concentration remaining in the silicon wafer is acceptable for solar cell applications.