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.