Multicrystalline silicon prepared by electromagnetic continuous pulling: recent results and comparison to directional solidification material

The electromagnetic continuous pulling (EMCP) is a new growth process competing with directional solidification for the production of massive silicon ingots. The advantages of the EMCP are higher production rates, no crucible consumption and a more uniform crystalline structure of the wafers. The present work is devoted to the characterization of the EMCP material by means of minority carrier diffusion length measurements (L) which allow the comparison between raw, annealed, phosphorus-diffused, annealed and gettered or hydrogenated wafers. The EMCP wafers are compared with conventionally cast wafers. It is shown that L is relatively high in the raw material, but L is degraded by annealings at temperatures higher than 600°C, while hydrogenation treatments drastically improve the material. In the present state, the EMCP silicon appears as a particular form of multicrystalline silicon materials with promising abilities. However, it requires low temperature processing steps or additional hydrogenation treatments to make low-cost and efficient solar cells.