GeO₂-doped SiO₂ sputtered thin films: Microstructure, stoichiometry, and optical properties

Radio frequency sputtering is a reliable and low-cost technique for the deposition of oxide thin films. Here we report on the nonreactive preparation of SiO₂ and SiO₂–GeO₂ films, which can be of interest in optics and optoelectronics. The deposition rate of SiO₂–GeO₂ is roughly three times higher than that of SiO₂. Secondary ion mass spectroscopy shows SiO nonstoichiometry in SiO₂ films, and the formation of Ge or Ge-based defects in SiO₂–GeO₂ samples. The best fits of the ellipsometric spectra confirm the nonstoichiometry of SiO₂ films, showing that SiO fraction (and the refractive index, n) tends to decrease by increasing the deposition time.