Hydrogen passivation and phosphorous gettering at different grain boundary types in multicrystalline silicon

Abstract

The dependency of minority charge carrier lifetime values at grain boundaries in multicrystalline silicon of different qualities on the grain boundary type after POCl3 gettering and/or firing of SiNx:H layers deposited by plasma enhanced chemical vapor deposition is analyzed. A new method to determine the coincidence site lattice grain boundary types on large scale is combined with spatially resolved lifetime-calibrated photoluminescence measurements and mappings of the interstitial iron concentration. Lifetime contrast values are calculated. A broader statistics than in former investigations is generated by this approach. Based on broad statistics, a dependency of the efficacy of all applied processes on the grain boundary type is shown -: higher coincidence site lattice indexes correlate with a decrease of median lifetime values after all applied processes. Hydrogenation of grain boundaries is found to be more effective in cleaner samples. The lifetime contrast values are dependent on the degree of contamination of the multicrystalline silicon material. In less contaminated samples they rather decrease after the processes, whereas in standard solar-grade material they increase after POCl3 diffusion and decrease again after subsequent hydrogenation. No correlation with the interstitial iron concentration could be found.