Hydrogenated amorphous silicon carbide films (a-SiC:H) were deposited using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) technique from a mixture of methane, silane and hydrogen, with diborane as the doping gas. The effect of the microwave power on the deposition rate was studied, and variations in the photoconductivity and dark conductivity were investigated in conjunction with film analysis using the Raman scattering technique. The conductivity increases rapidly to a maximum, followed by a rapid reduction at high microwave power. The ratio of the photoconductivity to the dark conductivity ((sigma(ph)/sigma(d)) peaks at a microwave power of approximately 600 W. Under conditions of high hydrogen dilution and increasing microwave power, Raman scattering analysis shows evidence of the formation and increase in microcrystalline silicon and diamond-like components in the films, the former of which may account for the rapid increase and the latter for the subsequent decrease in the conductivity.