To reduce the density of recombination centers, external gettering by phosphorus diffusion from a POCI3 source and hydrogénation were applied to 200 μm thick samples.
Gettering was carried out at 850°C or 900°C, for 120 or 240 mn. Hydrogénations result of the annealing of samples at 400°C for 30 mn in gas flow. Thanks to arrays of mesa diodes, it is found that minority carrier diffusion lengths (Ln) are neatly improved by the gettering. The improvements are higher at 900°C than at 850°C, they increase with gettering time and SIMS analyses indicate that they are due to the removing of Fe, Cu and Ni atoms.
Hydrogénation enhances Ln values in samples gettered at 850°C and the higher Ln the longer the gettering time. After hydrogénation, the values of Ln in the samples gettered at 850°C are comparable to those measured in samples gettered at 900°C. It is assumed that hydrogen is able to neutralize the activity of impurities which have not been gettered, like oxygen, and also that of residual metallic impurities.