N type multicrystalline silicon wafers from an upgraded metallurgical route

N-type silicon wafers present some definite advantages for photovoltaics, mainly due to the low capture cross sections of minority carriers for most metallic impurities. This peculiarity is beneficial for multicrystalline silicon (mc-Si) wafers. Most importantly, this peculiarity could be of a great interest when mc-Si ingots are produced directly from upgraded and purified metallurgical silicon feedstock. It is of a paramount importance to verify if the advantages of conventional n-type silicon also characterises n-type wafers provided by the direct metallurgical route. It is found, in raw wafers, that minority carrier diffusion lengths are 3 times higher in n-type than in p-type wafers, when the wafers are cut from the same ingot, which the bottom is p- type and the top is n-type. The results confirm the interest for n type silicon.