Effect of P-induced gettering on extended defects in n-type multicrystalline silicon

The electrical properties and the minority charge carrier recombination behaviour of grain boundaries (GBs) and intragrain dislocations in different n-type multicrystalline silicon (mc-Si) ingots were systematically studied through microwave-detected PhotoConductance Decay (mu W-PCD), Electron Beam Induced Current (EBIC) and PhotoLuminescence (PL) spectroscopy on as-grown samples and on samples submitted to P-diffusion step. It was confirmed that the overall quality of n-type mc-Si is high, indicating that n-type-Si is a valid source for photovoltaic applications. As expected, the average lifetime increases after the P-diffusion process, which induces impurity gettering effects at the external surfaces, like in the case of p-type samples, but an evident local increase of electrical activity of some GBs after that process was also observed using the EBIC mapping technique. Apparently, a redistribution of impurities occurs at the processing temperature and impurities are captured at the deepest sinks. In fact, while all GBs act as heterogeneous segregation/precipitation sites, some of them will compete with the external surfaces sinks, partly vanishing the effect of P-gettering. Last but not least, it was experimentally demonstrated that the average lifetime values measured with the RW-PCD technique well correlate with the recombination activity of GBs measured with the EBIC technique, showing the extreme importance of GBs on the effective lifetime of this material. Copyright (C) 2007 John Wiley & Sons, Ltd.