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

Abstract The BaSi 2 semiconductor is a promising candidate for an earth-abundant solar cell absorber. In this study, we have realized a crack-free BaSi 2 film by a simple thermal evaporation technique on a CaF 2 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 BaSi 2 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 BaSi 2 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 BaSi 2 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 BaSi 2 film are revealed by Hall measurement and the electron density and mobility are found to be 6 × 10 20 cm −3 and 0.04 cm 2 /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.