Photoluminescence characterization of phosphorus diffusion gettering in silicon substrates for solar cells

We have characterized the effectiveness of phosphorus (P) diffusion gettering in silicon wafers for solar cell substrates by the photoluminescence (PL) technique. Gettering with P diffusion at 950°C for 30 min increases the intensity of the band-edge emission, correlating positively with the minority carrier lifetime determined by the photoconductive decay method. We suggest that the lifetime is retarded by the presence of the nonradiative recombination centers and that the centers are gettered by the P diffusion. The spectral broadening and shift observed in a certain area of the gettered sample are explained by the residual stress of about 20 MPa at maximum. Microscopic PL mapping on a cross section of the substrate reveals that the depth of the denuded zone formed by gettering is about 30 μm. We demonstrate that gettering under the present condition is particularly useful in increasing the production yield of solar cells as a result of the improvement in quality of short-lifetime wafers