The effect of ammonia/acetylene ratio on characteristics of amorphous carbon films prepared by plasma enhanced chemical vapor deposition

The effect of different ammonia/acetylene (NH3/C2H2) ratio on the characteristics of amorphous carbon films prepared by radio-frequency plasma enhanced chemical vapor deposition is investigated. Five kinds of carbon films are prepared with NH3/C2H2 ratios of 0, 0.2, 0.5, 1, and 1.4. The radio-frequency power, substrate temperature, and working pressure were kept at 100 W, 298 K, and 28 Pa, respectively. The thickness of all kinds of carbon films was about 100 nm. Experimental results indicate that as the NH3/C2H2 ratio increases from 0 to 1.4, the nitrogen/carbon ratio in carbon films increases from 0 to 6.9%. The nitrogen–carbon bonds and sp2 carbon fraction of carbon films enlarge with increasing the NH3/C2H2 ratio, while the ordered degree, Young's modulus, and hardness of carbon films decrease. Furthermore, when the nitrogen-doped amorphous hydrogenated carbon, a-C:H(N), film was deposited on p-silicon (p-Si) substrate, the forward electrical resistance of a-C:H(N)/p-Si device decreases with increasing the NH3/C2H2 ratio. The quality factor (also called ideality factor) of a-C:H(N)/p-Si device is a measure of how closely this device follows the ideal diode equation, which has the best value of 1.3 at the NH3/C2H2 ratio of 1.4.

► As the NH3/C2H2 ratio increases, the nitrogen/carbon ratio in carbon films increases.
► The sp2 carbon fraction of carbon films increases with the NH3/C2H2 ratio.
► The ordered degree of carbon films decreases with increasing the NH3/C2H2 ratio.
► Young's modulus of carbon films decreases with increasing the NH3/C2H2 ratio.
► The a-C:H(N)/p-Si diode has an optimal electrical property at the N/C ratio of 6.9%.