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In this study, the influence of pulling rate on lifetime and impurity distribution in multicrystalline silicon has been investigated. Ingots have been pulled at different rates in a small scale Bridgman type furnace and were intentionally polluted with 50 ppma copper and 0.5 ppma of boron. The low lifetime regions are related to different defects, depending on the pulling rate. During the growth, the impurities interact with structural defects, such as grain boundaries or dislocations, leading to inhomogeneous distributions. The relative impacts of solid state diffusion and limited rejection at structural defects during the growth are investigated for each pulling rate. It is argued that solid state diffusion is the main mechanism for impurity inhomogeneity of fast diffusing elements like copper, while more slowly migrating elements, e.g. boron, show a more uniform distribution. |
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