Silicon (Si)-doped diamond-like carbon (DLC) was prepared on Si(100) and polymethyl methacrylate (PMMA) substrates using a C2H2-SiH4-Ar plasma immersion ion processing (PIIP) method. The chemical composition of the films was varied by adjusting the reactive gas-flow ratio of SiH4 to C2H2 during PIIP depositions. The influence of the Si dopant on the bonding structure, stress, and properties of the DLC films was investigated by using ion beam analysis techniques, Raman shift, ultraviolet/visible spectroscopy, and by analyzing the measured properties. The incorporation of Si up to 17.3 at. % produced a reduction in film stress and increased the density and optical band gap. The Si-doped DLC films also exhibited increased sp(3) bonding and higher hardness (25-28 GPa). Further increase in Si dopant, to above 22 at. %, caused a transformation from DLC to amorphous silicon carbide (a-SiC) that showed high hydrogen capacity, low hardness, and low stress. Pin-on-disk tribological tests df Si-doped DLC on PMMA showed greatly improved wear and friction properties related to the uncoated PMMA.