Microstructural, electrical, and optoelectronic properties of BaSi2 epitaxial films grown on Si substrates by close-spaced evaporation

BaSi2, an earth-abundant photovoltaic material with a limiting efficiency of 32 %, has the interesting property that grain boundaries do not significantly degrade the film properties. In this study, we investigated the microstructure and its effect on the electrical and optoelectronic properties of the BaSi2 films grown by close -spaced evaporation. Microstructural analysis confirmed the (100)-oriented epitaxial growth on both Si(100) and Si(111) substrates. In addition to conventional epitaxial relationships, lattice matching with the BaSi2(013) plane parallel to Si(110) was observed on Si(100) substrates. The density of the epitaxial domain boundary was found to decrease with increasing film thickness, increasing growth temperature, and using Si(100) substrates instead of Si(111). Hall effect measurements revealed the conductivity type transition at a temperature between 900 and 1000 & LCIRC;C and a decreasing tendency of carrier density with film thickness. There was no obvious cor-relation between mobility and grain boundary density, consistent with previous reports. Carrier recombination kinetics were evaluated by the microwave-detected photoconductivity decay method and the photoconductivity measurement under constant optical irradiation. Both analyses revealed weak negative correlations between excess carrier lifetime and grain boundary density, which clarified the superiority of large-grained BaSi2 films for photovoltaic applications.