Molecular beam epitaxy of band gap tunable ternary semiconducting silicides Ba_(1-x)Sr_xSi_2 for photovoltaic application

摘要

[100]-Oriented epitaxial and polycrystalline Ba_(1-x)Sr_xSi_2 films with various x values were grown by molecular beam epitaxy (MBE) on Si(111) and transparent fused silica substrates, respectively. The indirect absorption edge E_(edge) in Ba_(1-x)Sr_xSi_2 increased with increasing Sr composition, x, and reached approximately 1.40 eV when x = 0.52. However, the E_(edge) value was almost saturated for higher x values, and the formation of homogeneous Ba_(1-x)Sr_xSi_2 films was difficult for samples in which x > 0.6. Furthermore, phase separation was observed when x = 0.77. Using a thermodynamic model, the average phonon energy in BaSi_2 was estimated from the temperature dependence of the optical absorption edge to be approximately 25 meV.