Influence of hydrogen dilution on two-phase structure and electrical properties of hydrogenated silicon thin films

Hydrogenated silicon thin films with two-phase structure were prepared by plasma enhanced chemical vapor deposition (PECVD) at different hydrogen dilution ratios (R) and their microstructure and electrical properties were investigated. The results indicated that the film was amorphous when R was 10. As R increased, the film presented two-phase structure, and the thickness of the amorphous layer tended to thin and the transition to crystalline from amorphous started earlier. From XRD results, both crystallinity and average grain size of the films increased firstly and then decreased with increase of R, and at maximum values when R was 28.6. The change rule of dark conductivity and carrier density agreed with the change rule of crystallinity and average grain size, which showed a close positive relationship between electrical properties and the microstructure.