Apparatus and method for plasma deposition of thin film photovoltaic materials at microwave frequencies. The apparatus avoids unintended deposition on windows or other microwave transmission elements that couple microwave energy to deposition species. The apparatus includes a microwave applicator with conduits passing therethrough that carry deposition species. The applicator transfers microwave energy to the deposition species to activate or energize them to a reactive state conducive to formation of a thin film material. The conduits physically isolate deposition species that would react or otherwise combine to form a thin film material at the point of microwave power transfer. The deposition species are separately energized and swept away from the point of power transfer to prevent thin film deposition. Suitable deposition species include precursors that contain silicon, germanium, fluorine, and/or hydrogen. The invention allows for the ultrafast formation of silicon-containing amorphous semiconductors that exhibit high mobility, low porosity, little or no Staebler-Wronski degradation, and low defect concentration.