Compositional and structural variations of nitrogen doped amorphous carbon films grown by surface-wave mode microwave plasma CVD

Abstract

In this paper, we report the effect of acetylene (C 2 H 2 ) flow rates (5 to 20 sccm) on the compositional and structural variations of nitrogen doped amorphous carbon (a-C:N) thin films grown by surface-wave mode microwave plasma chemical vapor deposition at low temperature (≪100 °C). Argon was used as the main plasma source gas. The films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV/VIS/NIR spectroscopy and Fourier transform infrared spectroscopy (FTIR) measurements. The deposition rate of the films was typically 10 nm/min. The Tauc optical band gap of the films was in the range 1.6–1.8 eV. The XPS results show successful doping of nitrogen in the films, whereas N atomic concentration (at.%) into the films varied in the range of 23 to 35%. The N at.% in the films did not correlate with the increase of C 2 H 2 flow rate (i.e. decrease of nitrogen gas concentration). The maximum percentage of nitrogen take up was observed in the film grown at C 2 H 2 flow rate of 10 sccm. The FTIR results show enhanced contribution of C=C sp2 and C-N sp3 bonds with increasing C 2 H 2 flow rate. The increase of C-H vibration mode around 3300 cm−1 indicates the increase of sp3-bonded carbon in the films. The amorphous nature of the films was qualitatively understood from the Raman results.