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-Ge_{1 − x}C_x) 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 T_s, and some sp² CC bonds gain infrared activity. The fraction of sp³ GeC bonds rises with T_s, but the fraction of sp³ GeGe bonds gradually drops down. In addition, the refractive index and extinction coefficient increase with T_s. The film optical gap is seen to reach 1.15 eV when T_s is 200 °C. However, the optical properties of a-Ge_{1 − x}C_x films almost remain stable with the substrate temperature.