Dependence of Radio Frequency Power on Optical, Chemical Bonding and Photoluminescence Properties of Hydrogenated Amorphous Carbon Nitride Films

Hydrogenated amorphous carbon nitride films (a-CN
_x
:H) were prepared in a radio-frequency plasma enhanced chemical vapour deposition (r.f. PECVD) system with a parallel-plate configuration. The gas sources of CH
₄
and N
₂
were fixed at CH
₄
:N
₂
ratio of 1:3. The films were grown on glass and Si substrates on the grounded electrode at 100degC. The effect of r.f. power (varied between 0.71 - 3.54 W/cm
²
) on the optical, infrared (IR) absorption spectra and photoluminescence (PL) spectra of the a- CN
_x
:H films were studied. It was observed that the deposition rate increases linearly up to the r.f. power of 2.83 W/cm
²
, while the optical band gap (E
₀₄
) decrease exponentially in the whole range. This is proposed to be the effect of an increase in nitrogen incorporation into the sp
²
carbon clusters, as indicated by FTIR. The PL spectra consist of a band in the region of 2.10-2.40 eV, with peaks at approximately 2.23, 2.27 and 2.33 eV. The PL intensity of the films increases as the r.f. deposition power increases and is related to the increase of the sp
²
clusters with increasing nitrogen incorporation.