Abstract
Nanocrystalline silicon (nc-Si) thin films deposited by plasma-enhanced chemical vapor deposition at various silane flow rates ([SiH4]) are studied. The characterization of these films by high-resolution transmission electron microscopy, Raman spectroscopy and X-ray diffraction reveals that no film and very thin film is deposited at [SiH4]=0.0 and 0.1sccm, respectively. In addition, the structural change from an amorphous to a nanocrystalline phase occurs at around [SiH4]=0.2sccm. In this study, the importance of arriving species at surfaces and precursors is clearly demonstrated by the effect of a small addition of SiH4 on the frequency and width of a Raman peak and the structure of the grown film. The infrared spectroscopic analysis shows no hydrogen incorporation in the nc-Si film deposited at the low value of [SiH4]. However, the intensity of the peak around 2100cm−1 due to SiH decreases with increasing [SiH4]. All fabricated films give photoluminescence in the range between 1.7 and 2.4eV at room temperature, indicating enlargement of the band-gap energy. The presence of very small crystallites leads to the appearance of quantum confinement effects. The variations of the photoluminescence energy and spectral width are well correlated with the structural properties of the films such as crystallite size, crystalline volume fraction, and the density of Si-H bonds.
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