Realization of bulk multicrystalline silicon with controlled grain boundaries by utilizing spontaneous modification of grain boundary configuration

We succeeded in the realization of bulk multicrystalline silicon (mc-Si) with electrically inactive grain boundaries. A group of single-crystal Si wafers was used as an artificial multicrystalline seed with random grain boundaries. The crystal growth was carried out by the floating zone technique under ultrahigh vacuum at a growth rate of 1.0 mm/min. Under these conditions, most of the grain boundaries were spontaneously modified to ∑3. In contrast, random grain boundaries remained even after 40-mm growth when the growth rate was decreased to 0.2 mm/min. From these results, we suggest that the control of both the initial grain boundary configuration and the growth conditions is important to realize mc-Si with electrically inactive grain boundaries, which is a promising material for solar cell applications.