Thermodynamic analyses of thermal evaporation of BaSi2

Thermal evaporation is a useful method for the deposition of high-quality photovoltaic BaSi2 films. The elemental processes of BaSi2 film formation are, however, complicated due to vapor composition change during BaSi2 evaporation. In this study, we thermodynamically calculate the vapor composition for quantitative explanation of the evaporation process. The Ba and Si vapor fluxes are calculated from relative partial molar enthalpies of Ba and Si in Ba–Si melt. Calculations show a tendency of decreasing Ba vapor flux and increasing Si flux with decreasing mole fraction of Ba in Ba–Si melt, by which the vapor composition change from being Ba-rich to being Si-rich during thermal evaporation of BaSi2 is successfully explained. The calculation results are discussed by comparing with the depth profiles of evaporated films deposited at room temperature and deposition rate. The present results would be useful as a theoretical basis of thermal evaporation of BaSi2.