Simple method for significant improvement of minority-carrier lifetime of evaporated BaSi2 thin film by sputtered-AlOx passivation

A novel surface passivation of AlOx on BaSi2 thin films fabricated by vacuum evaporation for solar cell application has been developed. The minority-carrier lifetime of evaporated BaSi2 film is shorter than that of epitaxial film. This lifetime has been improved by forming AlOx passivation layer on the BaSi2 surface by RF sputtering of Al followed by oxidation in air. A drastic improvement of the lifetime upon the passivation of AlOx was observed up to 15 μs with 3-nm of AlOx layer after rapid thermal annealing at 475 °C for 15 min. The dependence of lifetime on passivation layer thickness disappeared for thickness higher than 9 nm, especially after annealing, showing the chemical passivation effect of AlOx. The result confirmed that AlOx is a promising passivation-layer for improving properties of BaSi2 film.