The effect of different radio-frequency powers on characteristics of amorphous boron carbon thin film alloys prepared by reactive radio-frequency plasma enhanced chemical vapor deposition Tsuen-Sung Chen, Shao-En Chiou, Sham-Tsong Shiue ⁎ Department of Materials Science and Engineering, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 402 Taiwan abstract article info Available online 7 November 2012 Keywords: Chemical vapor deposition Carbon Amorphous boron carbon thin film alloys Photovoltaic The effects of different radio-frequency (rf) powers on the characteristics of amorphous boron carbon (BC) thin film alloys on n-type silicon (n-Si) wafers prepared by reactive radio-frequency plasma enhanced chem- ical vapor deposition (rf-PECVD) are investigated. The reactive rf-PECVD was the combination of rf-PECVD and sputtering. Five kinds of amorphous BC thin film alloys were prepared with rf powers of 100, 200, 300, 400, and 500 W. Experimental results show that when the rf power increases from 100 to 500 W, the depo- sition rate of amorphous BC thin film alloys slightly decreases from 1.14 to 1.00 nm/s that is resulted from the increase of the B/C ratio. The amorphous BC thin film alloy prepared at the rf power of 300 W has a maximum graphitization degree and sp 2 carbon bonds, so it has the lowest energy band gap and electrical resistivity. All the amorphous BC thin film alloys prepared with different rf powers are p-type. When the amorphous BC thin film alloy prepared at the rf power of 300 W, the amorphous BC/n-Si diode possesses the lowest series resis- tance of 279 Ω and an ideality factor of 4.9; after annealed at 623 K, the series resistance and ideality factor of this diode reduce to 98 Ω and 2.47, respectively. When the amorphous BC thin film alloys were prepared at the rf power of 300 W, the built-in voltages of the amorphous BC/n-Si devices are 0.45 and 0.88 V for the amorphous BC thin film alloys before and after annealed at 623 K, respectively. When an additional native oxide of SiO 2 layer was prepared on the n-type silicon substrate surface, the power conversion efficiency and fill factor of amorphous BC/SiO 2 /n-Si devices are 1.04% and 88.3%, respectively. Hence, the amorphous BC thin film alloys prepared by reactive rf-PECVD have the potential applied to the fabrication of solar cells. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Amorphous carbon (a-C) films have several advantages including low-cost, easy to produce massively, semiconductor characteristics, and tunable band gap, which can be prepared with various character- istics by changing the sp 3 /sp 2 ratio [1,2]. Recently, a-C films were not only applied as protective layers or anti-reflective layers for solar cells, but also constructed as n-type carbon/p-type silicon or p-type carbon/n-type silicon heterojunction devices using doping method. Generally, the p-type amorphous carbon (p-C) films were prepared by doping boron [3–9] or metal elements [10–15] in a-C film using chemical vapor deposition (CVD) or physical vapor deposition (PVD) methods [4–9,16–23]. If the carbon materials with variable properties are demanded, CVD is better than PVD. However, the dop- ing sources (such as: BH 3 [5],B 2 H 6 , and C 3 H 9 B [9,18] gases) for CVD are usually dangerous. In this study, we will prepare the amorphous boron carbon (BC) thin film alloys using a reactive radio-frequency plasma enhanced chemical vapor deposition (reactive rf-PECVD) system. The purpose of this study is to prepare boron-doped amorphous carbon films. However, sometimes the B concentration in the films is much larger than 1%, so these films are called amorphous boron carbon thin film alloys [24]. The reactive rf-PECVD system was the combination of rf-PECVD and sputtering. A boron target was used as the dopant source, and a mixture of pure methane (CH 4 ) and argon (Ar) was selected as the precursor gas. The effect of different rf powers on the properties of amorphous BC thin film alloys will be investigated. The current density–voltage (J–V) and capacitance–voltage (C–V) characteristics of amorphous BC thin film alloys deposited on n-type silicon (n-Si) will be studied. Furthermore, the potential of amor- phous BC thin film alloys prepared by reactive rf-PECVD to construct the carbon-based solar cell will be also discussed. 2. Experimental details The experimental details proceeded as follows. First, 12.5 × 25 × 0.35 mm 3 n-type (100) Si wafers, 20×20×1 mm 3 stainless steel plates, and 12.5 × 25 × 1 mm 3 silica glass plates were cleaned in ultra- sonic bath of acetone, ethanol, and deionized (DI) water, in that order, Thin Solid Films 528 (2013) 86–92 ⁎ Corresponding author. Tel.: +886 4 22857211; fax: +886 4 22857017. E-mail address: stshiue@dragon.nchu.edu.tw (S.-T. Shiue). 0040-6090/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tsf.2012.09.091 Contents lists available at SciVerse ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf