Modeling of recombination strength at grain boundaries after phosphorus diffusion gettering and the effect of hydrogen passivation

We present a method for extracting local recombination rates from photoluminescence images of double side passivated wafers, using simulations of lateral charge carrier diffusion in two dimensions. By fitting the simulated carrier lifetime map with a calibrated photoluminescence image, the recombination profiles in bulk and at grain boundaries (GBs) can be extracted. This method can be used to quantify the GB recombination velocity even if the carrier concentration in bulk is simultaneously affected by recombination at multiple GBs. High performance multicrystalline wafers from a commercially cast ingot with low impurity concentrations were studied. The GBs were completely passivated applying a hydrogenation step simulated contact firing of a hydrogen rich silicon nitride (SiN) film. The bulk carrier recombination profile from simulations of carrier diffusion after phosphorus diffusion gettering is similar to the measured lifetime after phosphorus diffusion gettering and firing. This indicates that the main role of hydrogen passivation is deactivation of the GB recombination. No additional enhancement of the bulk lifetime is observed after hydrogen passivation.