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

Abstract

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.