Selective passivation of nitrogen clusters and impurities in photovoltaic GaInNAs solar cells

The selective passivation of lower energy defects related to nitrogen clusters and impurities is demonstrated using a low temperature UV-activated hydrogenation process. This is achieved without significant removal of substitutional nitrogen. In bulk reference materials the passivation of larger low-energy defects and the passivation of background impurity states is observed to remove the well-known s-shape variation in the luminescence energy versus temperature, related to nitrogen isoelectronic centers, while retaining the substitutional nitrogen in the alloy. This behavior is attributed to the passivation of donor electrons bound to the isoelectronic centers, resulting in significant band-to-band free carrier recombination across the GaInNAs energy-gap. Hydrogenated solar cells grown under non-optimum conditions to enhance the contribution of defect states where also evaluated. In these structures a significant decrease in impurity state luminescence is also evident, although the level of hydrogenation required is increased.