Electrical Conduction Properties of Hydrogenated Amorphous Carbon Films with Different Structures

• Main Authors: Masashi Tomidokoro, Sarayut Tunmee, Ukit Rittihong, Chanan Euaruksakul, Ratchadaporn Supruangnet, Hideki Nakajima, Yuki Hirata, Naoto Ohtake, Hiroki Akasaka
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Materials
• Subjects: hydrogenated amorphous carbon film; electrical conduction; CVD deposition; near-edge X-ray absorption fine structure; variable range hopping
• Online Access: https://www.mdpi.com/1996-1944/14/9/2355

Hydrogenated amorphous carbon (<i>a</i>-C:H) films have optical and electrical properties that vary widely depending on deposition conditions; however, the electrical conduction mechanism, which is dependent on the film structure, has not yet been fully revealed. To understand the relationship between the film structure and electrical conduction mechanism, three types of <i>a-</i>C:H films were prepared and their film structures and electrical properties were evaluated. The <i>sp</i>²/(<i>sp</i>² + <i>sp</i>³) ratios were measured by a near-edge X-ray absorption fine structure technique. From the conductivity–temperature relationship, variable-range hopping (VRH) conduction was shown to be the dominant conduction mechanism at low temperatures, and the electrical conduction mechanism changed at a transition temperature from VRH conduction to thermally activated band conduction. On the basis of structural analyses, a model of the microstructure of <i>a</i>-C:H that consists of <i>sp</i>² and <i>sp</i>³-bonded carbon clusters, hydrogen atoms and dangling bonds was built. Furthermore, it is explained how several electrical conduction parameters are affected by the carrier transportation path among the clusters.