Formation of high-photoresponsivity BaSi₂ films on glass substrate by radio-frequency sputtering for solar cell applications

The formation of high-photoresponsivity semiconducting films composed of earth-abundant elements on a SiO₂ substrate is of particular importance for large-scale deployment of solar cells. We investigated the deposition of high-photoresponsivity BaSi₂ films by radio-frequency sputtering on indium-tin-oxide (ITO), Ti, or TiN electrodes formed on a SiO₂ substrate. Raman spectroscopy and x-ray diffraction measurements revealed the formation of randomly oriented polycrystalline BaSi₂ films only on TiN/SiO₂ substrates at 570 °C–650 °C. In contrast, impurity phases such as Ba oxides and TiSi₂ were included when ITO and Ti layers were used, respectively. The photoresponsivity of the BaSi₂ films on TiN electrodes reached 1.1 A W⁻¹ at a wavelength of 790 nm under a bias voltage of 0.5 V applied between the front ITO and bottom TiN electrodes. This value is equivalent to the highest photoresponsivity ever achieved for BaSi₂ epitaxial films on Si(111) substrates by molecular beam epitaxy. (paper)