Raman spectroscopy of thin-film silicon on woven polyester

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Abstract

Thin-film silicon deposited by plasma-enhanced chemical vapour deposition (PECVD), encompasses both hydrogenated amorphous silicon (a-Si:H) and ‘nanocrystalline silicon’ (nc-Si), the latter being a two-phase mixture of discrete nanocrystallites in an amorphous matrix. It is distinguished from a-Si:H by a characteristic Raman spectrum. As the film structure moves from amorphous to more crystalline, the Raman TO phonon spectral region no longer consists of a broad amorphous peak at ∼480 cm−1 but instead has an obvious narrower peak located at higher wavenumber. The accepted signature peak for nc-Si lies between these two and most probably arises from the hexagonal, wurtzite structure of the nanocrystals. Here we use Raman spectroscopy to show how the structure of thin-film silicon on woven polyester is influenced by the substrate as well as by the deposition conditions. We find that the rough surface of the textile substrate enables nc-Si formation, provided that the correct deposition conditions are employed and that the substrate temperature does not exceed 210 °C. Although the gas mixture is the dominant parameter for determining the film structure, and input power also has a significant effect, we find that a specific combination of these interrelated parameters is essential to control the final structure.

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