Direct Photochemical Vapor Deposition of Hydrogenated Amorphous Silicon -Effects of Excitation Wavelengths and Source Gases-

Abstract

Hydrogenated amorphous silicon films have been prepared by a direct photochemical vapor deposition method using different excitation wavelengths and source gases. The films deposited with the combination of Si2H6+147 nm and Si2H6+185 nm showed good properties indicated by low value of Si-H2 bond density, Urbach energy and defect-state density compared with the films deposited with SiH4+147 nm. Results of simulation demonstrated that these good properties are caused by the smaller contribution of SiH2 and larger contribution of monoradicals to the deposition, and that interconnection of surface sites created from SiH2 is difficult compared with that from monoradicals. Detailed analysis of the simulation revealed that the reactions which control radical density are not those of initial photolysis but instead are secondary reactions, such as those involving atomic hydrogen.