Chemical bonding and optical properties of germanium–carbon alloy films prepared by magnetron co-sputtering as a function of substrate temperature

Amorphous non-hydrogenated germanium carbide (a-Ge1 − xCx) films have been prepared by magnetron co-sputtering system designed by ourselves. The chemical bonding and microstructure have been analyzed using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The optical properties of the films have been investigated by means of spectroscopic ellipsometry. The relationship between the chemical bonding and the optical properties has been explored. It has been found that all films with the constant carbon content are amorphous. The sp2 CC and sp3 GeC bonds increase with Ts, and some sp2 CC bonds gain infrared activity. The fraction of sp3 GeC bonds rises with Ts, but the fraction of sp3 GeGe bonds gradually drops down. In addition, the refractive index and extinction coefficient increase with Ts. The film optical gap is seen to reach 1.15 eV when Ts is 200 °C. However, the optical properties of a-Ge1 − xCx films almost remain stable with the substrate temperature.

► The details of synthesis of a-Ge1 − xCx films by magnetron co-sputtering are discussed.
► The chemical bonding and microstructure characterization are focused in details.
► The relationship between chemical bonding and optical properties is discussed in details.