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

Abstract

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 (μW-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 μLW-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 ©2007 John Wiley & Sons, Ltd.