Plasma deposition of carbon films at room temperature from C2H2,-Ar mixtures: anodic vs. cathodic films

Amorphous carbon films were deposited at room temperature on the anode and cathode of a radio-frequency glow discharge reactor by the dissociation of acetylene-argon mixtures. The film's properties ranged from low density, so ft polymer-like to higher density a-C:H. The changes in the atomic structur e, optical and electrical properties were studied as functions of the press ure. Anodic films are highly resistive, have a low refractive index (n appr oximate to 1.76-1.94) and a wide band gap (E-g approximate to 1.7-2.5 eV), whereas cathodic films are more conductive to (sigma approximate to 10(-12) -10(-9) S cm(-1)), have a higher refractive index (n approximate to 2.0-2.3 5) and a smaller band gap (E-g = 1-1.3 eV). The conductivity and activation energy of cathodic films can be controlled by the addition of phosphine or diborane to the gas mixture, suggesting that doping is possible in a-C:H a s in hydrogenated amorphous silicon. (C) 2001 Elsevier Science B.V. All rig hts reserved.