Two-channel gettering of recombination-active impurity in polycrystalline solar silicon

The features of the recombination-active impurity gettering in polycrystalline silicon have been studied. The research method included the formation of a porous silicon layer 0.5-2 μm in thickness on the backside of a silicon wafer, the deposition of aluminum layer 0.5-1 μm in thickness, and the thermal annealing at 700-950 oC during 30-60 min. The corresponding gettering model has been proposed, which includes the diffusion of iron atoms by means of two most probable independent channels: in the wafer bulk and along the grain boundaries. By comparing the theoretical results and experimental data, we established that 30% of gettered impurity atoms diffuse with a high rate along the grain boundaries, and 70% of them in the grain bulk.