Low temperature plasma production of hydrogenated nanocrystalline silicon thin films

Abstract

The hydrogenated nanocrystalline silicon (nc-Si:H) thin films were produced by capacitively-coupled plasma enhanced chemical vapor deposition (PECVD) technique at low substrate temperatures (Ts ≈ 40–200 °C). Firstly, for particular growth parameters, the lowest stable Ts was determined to avoid temperature fluctuations during the film deposition. The influence of the Ts on the structural and optical properties of the films was investigated by the Fourier transform infrared (FTIR), UV–visible transmittance/reflectance and X-ray diffraction (XRD) spectroscopies. Also, the films deposited at the center of the PECVD electrode and those around the edge of the PECVD electrode were compared within each deposition cycle. The XRD and UV–visible reflectance analyses reveal the nanocrystalline phase for the films grown at the edge at all Ts and for the center films only at 200 °C. The crystallinity fraction and lateral dark conductivity decrease with lowered Ts. FTIR analyses were used to track the hydrogen content, void fraction and amorphous matrix volume fraction within the films. The optical constants obtained from the UV–visible transmittance spectroscopy were correlated well with the FTIR results. Finally, the optimal Ts was concluded for the application of the produced nc-Si:H in silicon-based thin film devices on plastic substrates.