A process for making amorphous semiconductor alloy films and devices at high deposition rates utilizes microwave energy to form a deposition plasma. The alloys exhibit high quality electronic properties suitable for many applications including photovoltaic applications.The process includes the steps of providing a source of microwave energy, coupling the microwave energy into a substantially enclosed reaction vessel containing the substrate onto which the amorphous semiconductor film is to be deposited, and introducing into the vessel reaction gases including at least one semiconductor containing compound. The microwave energy and the reaction gases form a glow discharge plasma within the vessel to deposit an amorphous semiconductor film from the reaction gases onto the substrate. The reactions gases can include silane (SiH.sub.4), silicon tetrafluoride (SiF.sub.4), silane and silicon tetrafluoride, silane and germane (GeH.sub.4), and silicon tetrafluoride and germane. The reaction gases can also include germane or germanium tetrafluoride (GeF.sub.4). To all of the foregoing, hydrogen (H.sub.2) can also be added. Dopants, either p-type or n-type can also be added to the reaction gases to form p-type or n-type alloy films, respectively. Also, band gap increasing elements such as carbon or nitrogen can be added in the form of, for example, methane or ammonia gas to widen the band gap of the alloys.