The deposition of hydrogenated amorphous silicon carbide (a-SiC:H) films from a mixture of silane, acetylene, and hydrogen gas using the electron cyclotron resonance chemical vapor deposition process is reported. The variation of the deposition and film characteristics such as the deposition rate, optical band gap, photoluminescence, and the infrared (IR) absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of similar to 250 Angstrom/min at a moderate hydrogen dilution ratio of similar to 20 [hydrogen flow (sccm)/acetylene + silane flow (sccm)], and decreases in response to a further increase in the hydrogen dilution. There is no strong dependence of the optical band gap on the hydrogen dilution within the dilution range investigated (10 to 60), and the optical band gap calculated from the E-04 method varied marginally from similar to 2.85 to similar to 3.17 eV. The room temperature photoluminescence (PL) peak energy and intensity showed a prominent shift to a maximum value of similar to 2.17 eV corresponding to maximum PL intensity at a moderate hydrogen dilution of similar to 30. The PL intensity showed a strong dependence on the hydrogen dilution variation. IR absorption results show that films deposited at higher hydrogen dilution have more SI-C bonding.