Correlation between the optical bandgap and the monohydride bond density of hydrogenated amorphous silicon

In this study, a variation of the substrate temperature during plasma enhanced chemical vapor deposition of hydrogenated amorphous silicon is reported, which revealed a local minimum of the optical bandgap. It is shown, that the silicon monohydride bond density is more appropriate to describe this dependency than the commonly discussed layer properties hydrogen concentration and structural disorder. Furthermore, a high silicon monohydride bond density regime is suggested, in which the optical bandgap is independent of the bond density. This hypohesis explains previously published constant optical bandgaps under variation of the hydrogen concentration and structural disorder. •A minimum of the optical bandgap of a-Si:H under variation of the deposition temperature was observed•The silicon monohydride bond density is appropriate to describe this minimum•A high silicon monohydride bond density regime is suggested, in which the optical bandgap is independent of this bond density