Effects of fluorine incorporation on the structural and electrical properties of Diamond-like carbon

Kento Nakanishi, Jun Otsuka, Masanori Hiratsuka, Chen Chung Du, Akira Shirakura, Tetsuya Suzuki

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Diamond-like carbon (DLC) has widespread attention as a new material for its application to thin film solar cells and other semiconducting devices. DLC can be produced at a lower cost than amorphous silicon, which is utilized for solar cells today. However, the electrical properties of DLC are insufficient for this purpose because of many dangling bonds in DLC. To solve this problem, we investigated the effects of the fluorine incorporation on the structural and electrical properties of DLC. We prepared five kinds of fluorinated DLC (F-DLC) thin film with different amounts of fluorine. Films were deposited by the radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) method. C<inf>6</inf>H<inf>6</inf> and C<inf>6</inf>HF<inf>5</inf> were used as source gases. The total gas flow rate was constant and the gas flow rate ratio R (=C<inf>6</inf>H<inf>6</inf> / (C<inf>6</inf>H<inf>6</inf> + C<inf>6</inf>HF<inf>5</inf>)) was changed from 0 to 1 in 0.25 ratio steps. We also prepared nitrogen doped DLC (F-DLC) on p-Si using N<inf>2</inf> gas as a doping gas to form nitrogen doped DLC (F-DLC) / p-Si heterojunction diodes. X-ray photoelectron spectroscopy (XPS) showed that fluorine concentration in the DLC films was controlled. Moreover, the XPS analysis of the CI s spectrum at R=2/4 showed the presence of CF bonding. At R=l, CF<inf>2</inf> bonding was observed in addition to CF bonding. The sheet resistivity of the films changed from 3.07x10<sup>12</sup> to 4.86><10<sup>9</sup> Ω. The minimum value was obtained at R=2/4. The current-voltage characteristics indicated that nitrogen doped F-DLC of 2/4 and p-Si heterojunction diode exhibited the best rectification characteristics and its energy conversion efficiency had been maximized. This is because of a decrease of dangling bonds density by ESR analysis and an increase of sp<sup>2</sup> structures by Raman analysis. When the fluorine is over certain content, the sheet resistivity increases because chain structures become larger, which is due to the CF<inf>2</inf> bonding in F-DLC prevents ring structures. Many C<inf>2</inf>F<inf>4</inf> species were observed and it may become precursors of the chain structure domains, such as (CF<inf>2</inf>)<inf>n</inf> this study, we revealed effects of fluorine incorporation on DLC and succeeded in increasing its conductivity and improving rectification characteristics of DLC/ p-Si heterojunction diodes. Our results indicate that DLC fluorination is effective for the semiconducting material, such as solar cell applications. copy; 2015 Materials Research Society.

Original languageEnglish
Title of host publicationMaterials Research Society Symposium Proceedings
PublisherMaterials Research Society
Number of pages6
ISBN (Print)9781510806153
Publication statusPublished - 2015
Event2014 MRS Fall Meeting - Boston, United States
Duration: 2014 Nov 302014 Dec 5


Other2014 MRS Fall Meeting
CountryUnited States


ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering
  • Mechanics of Materials

Cite this

Nakanishi, K., Otsuka, J., Hiratsuka, M., Du, C. C., Shirakura, A., & Suzuki, T. (2015). Effects of fluorine incorporation on the structural and electrical properties of Diamond-like carbon. In Materials Research Society Symposium Proceedings (Vol. 1734, pp. 40-45). Materials Research Society. https://doi.org/10.1557/opl.2015.306