Comparative study of optical properties of germanium carbon films deposited by reactive sputtering and co-sputtering

Amorphous hydrogenated germanium carbon (a-Ge1 − xCx:H) films were prepared by both reactive sputtering of a pure Ge target in CH4 + H2 + Ar mixture and co-sputtering of Ge/Graphite target in H2 + Ar mixture. Their composition, chemical bonding and optical properties were investigated and through comparison it is found that the deposition rate of the films deposited by reactive sputtering is considerably larger than that deposited by co-sputtering. Moreover, the optical gap of the a-Ge1 − xCx:H films deposited by reactive sputtering is lower compared with that of co-sputtering at the same C content which is mainly due to the relatively low content of GeC bonds that the co-sputtering fabrication process is more favorable to form the GeC bonds than reactive sputtering. Besides, the refractive index of the films appears as the similar rule of the optical band gap both due to the content of GeC bonds and the density of the films. Through the analysis of X-ray photoelectron spectroscopy (XPS), it is found that the formation of GeC bonds in the films is promoted by high energy C sputtered from graphite target.