Effects of hydrogen and substrate temperature on the chemical bonding and optical properties of germanium carbon films deposited by reactive sputtering

Abstract

Germanium carbon (Ge1−xCx) films were prepared by radio frequency (RF) reactive magnetron sputtering of a pure Ge (111) target in a CH4+H2+Ar mixture and their composition, chemical bonding, optical properties were investigated as a function of substrate temperature and gas flow ratio of H2/(CH4+Ar). The results show that the deposition rate decreased almost linearly with increasing the substrate temperature and gas flow ratio. And the optical gap of the Ge1−xCx films decreased from 1.5 to 0.9eV due to the drop in the carbon content of the films as the substrate temperature was increased with the relative content of GeC bonds decreasing. The optical gap first decreased and then increased as the gas flow ratio was increased from 0 to 1.125. Through the analysis of XPS spectrum, it is found that the formation of GeC bonds in the films was promoted both by low substrate temperature and by high atomic hydrogen content in the working gas mixture near the growth surface. Especially in high H2 concentration, the optical gap shows an abnormal increase due to the increase of the formation of sp3-hybridized C and high concentration of CH bonds.