Effect of deposition pressure on the properties of amorphous carbon films by hot-filament chemical vapor deposition

Deposition pressure is an important factor for the preparation of amorphous carbon (a-C) films through vacuum method. However, researches about the properties, especially optical and electrical properties of a-C films influenced by deposition pressure are still rare. In this work, hot-filament chemical vapor deposition (HFCVD) was used to deposit conductive a-C films under different deposition pressure conditions. As deposition pressure raised from 5 to 160 Pa, a structural transition from a-C to nanocrystalline graphite that led to the increase of cluster size, sp2 content and crystalline quality of a-C films was observed. The hybrid structure composed of amorphous and nanocrystalline phases was also revealed by high-resolution transmittance electron microscope. The mobility, transmittance and conductivity of films increased while the optical gap and carrier concentration decreased by elevating the deposition pressure. As a result, a-C films prepared at 160 Pa showed the best property with a roughness of 0.412 nm, a transmittance of 67%, an optical bandgap of 1.25 eV, a resistivity of 75 μΩ m and a mobility of 3.17 cm2 V−1 s−1, which is comparable to those prepared through other methods. The small roughness, good transmittance and low resistivity implied that high quality a-C films can be prepared through HFCVD method by adjusting the deposition pressure.