Formation of antireflection structures for silicon in near-infrared region using AlOx/TiOx bilayer and SiNx single-layer

Antireflection (AR) layers for Si were investigated for applications in optical communication in the wavelength range of 1270-1330 nm. The Essential Macleod software was used to find the optimal thicknesses of the AR coatings with two different structures of AlOx/TiOx bilayer and SiNx single-layer. The simulations revealed reflectances lower than 0.5% for both AlOx/TiOx and SiNx AR structures. Furthermore, atomic layer deposition and plasma-enhanced chemical vapor deposition were used to grow the AlOx/TiOx and SiNx layers, respectively. For the fabricated structures, average reflectances of 0.2% (AlOx/TiOx) and 0.3% (SiNx) were achieved in the wavelength range of 1270-1330 nm. For the AlOx/TiOx bilayer, a lower transmittance of ~88% was obtained, compared with that of the SiNx single-layer of ~99%. An additional air annealing at 300 °C for 2 h led to a crystallization of the amorphous TiOx into anatase phase, which yielded an improved transmittance of ~99%, comparable with that of the SiNx single-layer structure. X-ray photoelectron spectroscopy revealed that the oxidation state of Ti in TiOx influenced the absorption in the near-infrared region.