Medium-range order in a-Si:H films prepared from hydrogen diluted silane

A systematic and detailed analysis of the influence of hydrogen (H2) dilution of silane (SiH4) on the structural properties of thin hydrogenated silicon (Si:H) films was carried out. The Si:H films were prepared by plasma enhanced chemical vapour deposition method at different H2 to SiH4 flow ratios (R) ranging from R¿=¿0 to 40. A detailed structural analysis was carried out by X-ray diffraction (XRD). In order to suppress the XRD intensity from the substrate, Si:H films were deposited onto a [100]-oriented single-crystalline silicon substrate and XRD was carried out with a thin-film attachment. The XRD analysis demonstrated that the first diffraction peak in the Si:H films corresponded to the signal from silicon hydride (Si4H) ordered domains having tetragonal lattice structure. The full width of half maximum (FWHM) of the peak was decreasing with increasing H2 dilution, and remained nearly constant for R¿¿¿20. The FWHM values confirmed that the Si:H films grown at R¿¿¿20 are more ordered than films deposited at lower R. This trend was confirmed by the Raman spectroscopy from the analysis of the shift of the Raman amorphous peak.