Structural and electrical characterizations of crack-free BaSi2 thin films fabricated by thermal evaporation

•Thermal evaporation of BaSi2 on a CaF2 substrate with a Si supply layer•Crack-free film owing to the matching of thermal expansion coefficients•Electron density and mobility of the evaporated film are 6 × 1020 cm− 3 and 0.04 cm2/V ⋅ s, respectively.•Twenty-times longer carrier lifetime (0.6 μs) than evaporated films on glass substrates without Si supply layers

The BaSi2 semiconductor is a promising candidate for an earth-abundant solar cell absorber. In this study, we have realized a crack-free BaSi2 film by a simple thermal evaporation technique on a CaF2 substrate at a growth temperature of 500 °C for electrical characterization. A Si layer preliminarily formed on the substrate by sputtering is a key to obtain stoichiometric BaSi2 film. Detailed structural characterization of the evaporated films with different Si layer thicknesses by X-ray diffraction, scanning and transmission electron microscopy demonstrates that a crack-free 370-nm-thick BaSi2 film is formed by consuming the Si layer. It is observed that the 90-nm-thick bottom part is microcrystalline and contains Ar atoms, which come from Si deposition atmosphere. The surface of the BaSi2 layer is found to be covered by an amorphous Si layer due to Si-rich vapor at the last stage of evaporation. Electrical properties of the BaSi2 film are revealed by Hall measurement and the electron density and mobility are found to be 6 × 1020 cm−3 and 0.04 cm2/V⋅s, respectively. Owing to a better crystalline quality contributed by the preliminarily-deposited Si layer, minority-carrier lifetime of the evaporated film (0.6 μs) is twenty times longer than previous films on glass substrates.