Evaluation of Band Structure of Single Crystalline Si-Rich SiSn thin Film

We evaluated the bandgap energy and optical properties of single-crystalline silicon-tin (Si 1- x Sn x ) thin films utilizing Photoluminescence (PL), spectroscopic ellipsometry (SE), and X-ray photoelectron spectroscopy (XPS). The PL and SE results showed that the indirect and direct bandgap energy decrease with increasing Sn fraction. Furthermore, the change in the direct bandgap energy is larger than the indirect bandgap energy. This shows that Si 1- x Sn x approaches the direct transition type. Then, the Sn fraction from the indirect-to-direct bandgap is estimated to be 47.2%. In addition, XPS results showed that the difference in valence band maximum between Si 1- x Sn x and pure Si increased depending on Sn fraction. This is responsible for the decrease in the indirect and direct bandgap energy.