DIRECT PHOTOCHEMICAL VAPOR-DEPOSITION OF HYDROGENATED AMORPHOUS-SILICON - EFFECTS OF EXCITATION WAVELENGTHS AND SOURCE GASES

Hydrogenated amorphous silicon films have been prepared by a direct ph otochemical vapor deposition method using different excitation wavelen gths and source gases. The films deposited with the combination of Si2 H6+147 nm and Si2H6+185 nm showed good properties indicated by low val ue of Si-H-2 bond density, Urbach energy and defect-state density comp ared with the films deposited with SiH4+147 nm. Results of simulation demonstrated that these good properties are caused by the smaller cont ribution of SiH2 and larger contribution of monoradicals to the deposi tion, and that interconnection of surface sites created from SiH2 is d ifficult compared with that from monoradicals. Detailed analysis of th e simulation revealed that the reactions which control radical density are not those of initial photolysis but instead are secondary reactio ns, such as those involving atomic hydrogen.