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

Published online by Cambridge University Press:  30 March 2015

Kento Nakanishi ,
Jun Otsuka ,
Masanori Hiratsuka ,
Chen Chung Du ,
Akira Shirakura  and
Tetsuya Suzuki
Kento Nakanishi
Affiliation:
Center for Science of Environment, Resource and Energy, Keio University, Yokohama, Kanagawa, Japan
Jun Otsuka
Affiliation:
Center for Science of Environment, Resource and Energy, Keio University, Yokohama, Kanagawa, Japan
Masanori Hiratsuka
Affiliation:
Nanotec Corporations, Kashiwa, Chiba, Japan
Chen Chung Du
Affiliation:
Industrial Technology Research Institute, Hsinchu, ROC
Akira Shirakura
Affiliation:
Center for Science of Environment, Resource and Energy, Keio University, Yokohama, Kanagawa, Japan
Tetsuya Suzuki
Affiliation:
Center for Science of Environment, Resource and Energy, Keio University, Yokohama, Kanagawa, Japan
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Abstract

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. C6H6 and C6HF5 were used as source gases. The total gas flow rate was constant and the gas flow rate ratio R (=C6H6 / (C6H6 + C6HF5)) was changed from 0 to 1 in 0.25 ratio steps. We also prepared nitrogen doped DLC (F-DLC) on p-Si using N2 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 C1s spectrum at R=2/4 showed the presence of CF bonding. At R=1, CF2 bonding was observed in addition to CF bonding. The sheet resistivity of the films changed from 3.07×1012 to 4.86×109 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 sp2 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 CF2 bonding in F-DLC prevents ring structures. Many C2F4 species were observed and it may become precursors of the chain structure domains, such as (CF2)n.

In this study, we revealed effects of fluorine incorporation on DLC and succeeded in increasing its conductivity and improving rectification characteristics of DLC/ p-Si hetero-junction diodes. Our results indicate that DLC fluorination is effective for the semiconducting material, such as solar cell applications.

Keywords

plasma-enhanced CVD (PECVD) (deposition)diamondfilm
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1734: Symposium R – Diamond Electronics and Biotechnology—Fundamentals to Applications , 2015 , mrsf14-1734-r03-12
Copyright
Copyright © Materials Research Society 2015 

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