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The structural, optical, and transport properties of hydrogenated amorphous carbon films deposited on the grounded electrode under different dilutions (pure CH4, CH4+H2, and CH4+Ar) in radio frequency powered plasma enhanced chemical vapor deposition process have been studied. Though all the samples deposited were observed to be polymer-like carbon, they have different optical and transport properties. While some of the samples were highly conductive under dark (∼10−1Scm−1 at room temperature), others exhibited very low (<10−12Scm−1) dark conductivity and were photoconductive (∼10−9–10−10Scm−1) only under ultraviolet (UV) light (wavelength λ<250nm). There appears to be a close link between the transport properties and optical absorption. Based on optical absorption, we propose two possible models for the distribution of the density of states involving the π and σ states. The evolution of these states and of the deep defect absorption has a profound impact on the transport properties and particularly on the UV photoconductivity. Comparing the two models, it seems more probable that the UV photoconductivity (for photon energy >4.96eV) is rather linked to transitions involving the σ-σ* states.

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