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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 vapour deposition (ECR-CVD) process is reported. The variation of the deposition and film characteristics such as the deposition rate- optical bandgap, photoluminescence and the infra-red (IR) absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of ~25 nm/min at a moderate hydrogen diIution ratio of ~20 [hydrogenflow (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 bandgap on the hydrogen dilution within the dilution range investigated (10 to 60), and the optical bandgap calculated from the E04 method varied marginally from ~2.85 eV to ~3.17 eV. The room temperaturephotoluminescence (PL) peak energy and intensity shows a prominent shift to a maximum value of ~2.17 eV corresponding to maximum PL intensity at a moderate hydrogen diIution of ~30.The PL intensity shows a strong dependence on the hydrogen dilution variation. IR absorption results show that films deposited at higher hydrogen dilution have more Si-C bonding.