Results obtained for deposition of hydrogenated amorphous silicon by infrared lasers and ultraviolet (UV) lasers are compared with plasma deposition data. Mechanistic information is extracted from the results obtained recently byinsitudiagnostic techniques andexsituanalysis of the film properties. A similar mechanism is proposed for the first stage of the deposition process including gas phase chemistry and chemisorption of film precursors for soft and energized processing. Characteristic differences are observed in the second dehydrogenation and solidification stage of the deposition process. Compared with CO2laser processing UV photons induce additional dehydrogenation The plasma environment has the potential to restrict the formation of polyhydrides and leads to the most efficient dehydrogenation.