A-Si/SiO2 nanolaminates for tuning the complex refractive index and band gap in optical interference coatings

A-Si/SiO2 nanolaminates are deposited by magnetron sputtering and show a decreasing absorption when the a-Si single-layer thickness is reduced from 2.4nm to 0.7nm. Moreover, an increase of the Tauc band gap by 0.18eV is measured. Experimental Tauc band gaps are compared to calculated effective band gaps, utilizing a numerical Schrödinger solver. Further, it is demonstrated that the refractive index can be controlled by adjusting the a-Si and SiO2 single-layer thicknesses in the nanolaminates. The nanolaminates are optically characterized by spectroscopic ellipsometry, transmittance, and reflectance measurements. Additionally, TEM images reveal uniform, well-separated layers, and EDX measurements show the silicon and oxygen distribution in the nanolaminates.