A method is described of depositing film of an amorphous or microcrystalline material, for example silicon, from a plasma on to a substrate. Microwave energy is introduced into a chamber as a sequenceof discrete microwave pulses, a film precursors gas is introduced into the chamber as a sequence of discrete gas pulses, and gas for generating atomic hydrogen is supplied to the chamber at least during each microwave pulse. Each microwave pulse is followed in non-overlapping fashion with a precursor gas pulse, and each precursor gas pulse is followed by a period during which there is neither a microwave pulse nor a precursor gas pulse.