Quantitative determination of element distributions in silicon based thin film solar cells using SNMS

Abstract

The determination of elemental distributions in thin film solar cells based on amorphous silicon using electron beam SNMS is possible by quantifying the measured ion intensities. The relative sensitivity factors (RSFs) for all elements measured have to be known. The RSFs have been determined experimentally using implantation and bulk standards with known concentrations of the interesting elements. The measured RSFs have been compared with calculated RSFs. The model used for the calculation of the RSFs takes into account the probability for electron impact ionization and the dwell time of the neutrals inside the postionization region. The comparison between measured and calculated RSFs shows, that this model is capable to explain the RSFs for most elements. Differences between calculated and measured values can be explained by the formation of hydride and fluoride molecules (in case of H and F) and influences of the angular distribution of the sputtered neutrals in case of Al. The experimentally determined RSFs have been used for a quantification of depth profiles of the i-, buffer-, p- and front contact layers of a-Si solar cells.