Impact of sublayer thickness and annealing on silicon nanostructures formation in a-Si:H/a-SiNx:H superlattices for photovoltaics

In this work, we synthesized amorphous multilayered a-Si:H/a-SiNx:H superlattices with different thickness of sublayers grown on silicon and quartz substrates by PECVD method at low power density (60 mW/cm2) and substrate temperature (250 °C) using nitrogen and silane gases as reactive precursors. Subsequently, the post-deposition annealing of these structures, composed of alternating layers of a-Si:H and a-SiNx:H, was carried out up to 1100° in vacuum to form silicon nanostructures. The dependence of the structural and chemical bonding characteristics of prepared superlattices on the silicon sublayer thickness and post-deposition annealing temperature was investigated. The formation of silicon nanostructures was confirmed by transmission electron microscopy, X-ray diffraction measurement and Raman scattering spectroscopy. Changes in bonding configuration during the annealing were carried out by Fourier transform infrared spectroscopy. Optical properties were studied by UV-Vis spectroscopy. XRD, Raman and TEM measurements show that the crystallization process of a-Si:H sublayers strongly depends on the thickness of initial a-Si:H sublayers and the post-deposition treatment process. It was found that a higher crystallization temperature for the thinner a-Si:H sublayers is needed. Results clearly show that structural and optical characteristics of these systems can be controlled by deposition parameters and post-deposition annealing conditions.