Fluorinated and hydrogenated amorphous silicon‐carbon alloys (a‐SiC:H,F) are produced by glow discharge decomposition of SiF4‐CH4‐H2mixture. Small amount of CH4in SiF4‐H2mixture are enough to produce silicon carbon alloys having optical gap ranging between 1.8 and 2.6 eV. Materials, having 1.95 eV band gap and exhibiting optoelectronic properties typical of state of arta‐SiC:H, are deposited under plasma modulation conditions. ©1996 American Institute of Physics.