Silicon Ingot Characterization by Quasi-Steady-State Photoconductance

The detailed knowledge of the distributions of carrier lifetimes, impurities and crystal defects in silicon ingots is key for understanding and improving wafer quality as well as solar cell processing steps. In this work, we have applied a quasi-steady-state photoconductance tester developed for the use on ingots to the measurement of lifetimes and dissolved iron concentrations along a p-type multicrystalline silicon block. The iron concentrations are determined by lifetime measurements taken before and after flashing the block to break the iron-boron pairs. Measurement of the iron-boron re-pairing time confirms that the changes in the lifetime after flashing the block are indeed due to the presence of dissolved iron impurities. The measured Fe profile along the block is in qualitative agreement with those reported in previous work, and fits the expected trend due to impurity segregation. The lifetimes are also compared with a calibrated PL image on the same ingot, which shows similar qualitative trends, but lower lifetime magnitudes due to the lower injection level in the PL measurement.