Compositional microcharacterization of electrically active and chemically passivated silicon grain boundaries

Abstract

The mechanisms controlling the electrical passivation of grain boundaries in polycrystalline silicon, using the incorporation of hydrogen in these regions, are investigated. For the first time, direct and correlated microelectrical and microcompositional measurements of the effects of hydrogen on Si grain boundaries are presented. The detection, spatial mapping and quantification of hydrogen within the polycrystalline Si has been accomplished by a specially developed secondary ion mass spectrometry (SIMS) method. In this, selected secondary ion species corresponding to elements of molecules of interest are measured and stored (indexed for intensity, type, and spatial origin) digitally for an incremental volume encompassing the region of interest (i.e., the grain boundary plane). These data are utilized to determine the diffusion coefficients (temperature dependencies, activation energies, and preexponential coefficient terms) of hydrogen in the grain boundaries and the grains as functions of the processing parameters. The effects of the hydrogen passivation process on the performance of solar cells are discussed.