Recombination activity of Σ3 boundaries in boron-doped multicrystalline silicon: Influence of iron contamination

The impact of the boundary plane and impurity contamination on the recombination activity of Σ3 boundaries in multicrystalline silicon (mc-Si) was studied by means of electron-beam-induced current (EBIC) technique. In the as-grown contamination-free mc-Si, the EBIC contrast of different Σ3 boundaries was in the order of Σ3{111}<Σ3{110}<Σ3{112}. This order may be attributed to the difference in the defect density of the Σ3 boundaries due to the effect of the boundary plane. But the maximum EBIC contrast did not exceed 2% at 300K, suggesting that the Σ3 boundaries are originally electrically inactive and the boundary plane has no significant effect on their recombination activity. When contaminated with Fe at 900°C, the EBIC contrasts of the Σ3{110} and Σ3{112} increased at 300K, whereas that of the Σ3{111} was still weak (<3%). This variation in the EBIC contrast may be related to the effect of boron and it is also indicated that the Σ3{111} has the weakest gettering ability. When contaminated with Fe at 1100°C, the EBIC contrasts of all the Σ3 boundaries continued to increase and bright-denuded zones developed around the boundaries. The Σ3 boundaries in the 1100°C air-cooled mc-Si showed stronger EBIC contrasts and broader denuded zones than those in the 1100°C quenched one. This phenomenon was explained in terms of the precipitation of Fe. The precipitation of Fe at grain boundaries (GBs) was affected by both the GB type and cooling rate, that is, Fe is easier to form precipitates onto the Σ3{110} and Σ3{112} boundaries during slow cooling.