This study investigates the effect of ammonia/methane (NH3/CH4) mixtures on characteristics of nitrogen-doped amorphous hydrogenated carbon (a-C:H(N)) films prepared by plasma enhanced chemical vapor deposition. The a-C:H(N) films with identical thickness are deposited on p-type silicon (p-Si) substrates using different NH3/CH4 ratios. These a-C:H(N)/p-Si junctions are a potential candidate to use in electronic or photoelectronic devices. The microstructures, optical properties, and mechanical properties of a-C:H(N) films are evaluated. Furthermore, the residual stresses in a-C:H(N) films, and also, the current density-voltage and capacitance density-voltage behaviors of a-C:H(N)/p-Si devices are investigated. Experimental results indicate that as the NH3/CH4 ratio increases from 0 to 0.2, the nitrogen/carbon ratio increases from 0 to 5.4%. The nitrogen-carbon bonds, nitrogen-hydrogen bonds, and sp(2) carbon fraction of carbon films enlarge with increasing NH3/CH4 ratio, while the deposition rate, ordered degree, optical band gap, reduced Young's modulus, hardness, and residual stress of carbon films decrease. The a:C:H(N)/p-Si device has an optimum electrical property at the NH3/CH4 ratio of 0.15 (or at the N/C ratio of 4.7%). Finally, the results of this study are compared with those reported in literatures. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.051202jes] All rights reserved.