Out-diffusion of metal from grain boundaries in multicrystalline silicon during thermal processing

For multicrystalline silicon, the principal understanding of gettering and other high temperature processes is important for the optimisation of the solar cell performance. We studied this issue by examining the minority carrier density distribution before and after thermal oxidation with spatially resolved and injection dependent lifetime methods. Experiments with different temperature ramps and times were done on two different starting materials. On pre-gettered material, results led to the hypothesis, that grain boundaries decorated with precipitates emit interstitial iron atoms into their vicinity. Simulations strongly supported this theory of out-diffusion. On the material without pre-gettering more processes go on simultaneously. Out-diffusion could be found again, but mostly superimposed by other processes, allocated to surface gettering or clustering.