The effect of rf power and substrate temperatureTson the optical, electrical, and structural properties ofa‐Si1−xCx:H alloy films deposited in the new hot‐plasma‐box glow‐discharge reactor are reported. The rate of deposition as well as the total fractionxof the carbon incorporated in the alloy films were found to vary in a direct proportion with the rf power, whereas the same parameters displayed an inverse proportionality to the changes inTs. Second, the hydrogen concentration in the alloy films was found to decrease with the increase in substrate temperature while it did not show appreciable variation with the changes in rf power. Next, the structural disorder in the amorphous network was observed to increase rapidly with increase in rf power although a slight improvement was made possible by elevating theTs. The analysis of Raman scattering and optical band‐gap measurements on these alloy films indicates that a large proportion of the Si—C and C—C bond pairs favors the diamondlike (sp3) bonding configuration at low rf power when theTsis high, whereas the graphitelike (sp2) C—C clusters show up only at high rf power values when theTsis low. The efficiency of C incorporation in these alloy films prepared by the present technique appears to be better than its best possible magnitude in the conventional open parallel‐plate glow‐discharge‐deposition systems.