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

► Germanium carbon films were prepared by reactive sputtering in a CH4 + H2 + Ar mixture. ► Deposition rate, chemical bonding and optical properties were investigated. ► The effects of composition and chemical bonding on optical gap were investigated. ► we found that high H2 can broaden the optical band gap.