The role of hydrogen in the growth of amorphous hydrogenated carbon

Abstract

We have investigated the role of hydrogen atoms, ions, and molecules in the growth of amorphous hydrogenated carbon by plasma chemical vapor deposition. By varying the ratio of CH4 to H2 in the feedstock, we varied the concentration of hydrogen atoms, ions, and molecules in the plasma. We observed that with increasing hydrogen concentrations in the plasma, the film growth rate decreases, the hydrogen concentration in the grown film decreases, and the optical bandgap decreases. We interpret these results in term of increased hydrogen etching of the carbon-hydrogen bonds that terminate the growing graphite-like crystallites. This leads to larger graphite-like crystallites, lower hydrogen concentrations in the growing film, and consequently, smaller optical bandgaps.