The effect of radio frequency power on the structural and optical properties of a-C:H films prepared by PECVD
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Xinyu Tan,a) Lihua Jiang,b) Ting Xiao, and Peng Xiang College of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials (CTGU), China Three Gorges University, Yichang 443002, China
Wensheng Yan Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology, Karlsruhe 76344, Germany (Received 16 August 2016; accepted 20 December 2016)
Hydrogenated amorphous carbon (a-C:H) films with a designed buffer layer of amorphous hydrogenated silicon carbide on the substrates were fabricated by plasma enhanced chemical vapor deposition (PECVD). The effect of radio frequency (RF) power on the structural and optical properties of a-C:H films was investigated. The ratios of sp3 to sp2 of carbon atoms and hydrogen contents in the RF power range of 75–175 W are determined and a similar trend as a function of power. The increase of sp3 to sp2 ratio leads to the increase of transmittance and optical gap of a-C:H films. a-C:H film under an RF power of 175 W possesses high transmissive ability (.80%) in the visible wave length, even the highest transmittance value of about 94.2% is achieved at the wave length 550 nm. These results show the optimal a-C:H films which are promising for the applications in the area of solar cells acting a window layer and antireflection layer.
I. INTRODUCTION
Hydrogenated amorphous carbon (a-C:H) films consist of carbon atoms of both graphitic type bonding (sp2) and diamond type tetrahedral bonding (sp3). Similar to their counterparts, like diamond, graphite, and hydrocarbon polymers, The hydrogenated amorphous carbon films demonstrate some extraordinary properties such as excellent mechanical hardness, heat conduction, high electrical resistance, high transmittance of infrared (IR) and ultraviolet (UV) light-cut filter, and optical transparency in the infrared region.1–4 These properties enable a-C:H films to be of wide applications in magnetic media, optical lens, biomedical and micro-/nano-electromechanical devices, and optical coating.5–9 In addition, a-C:H films are promising as antireflection coating, p-type window layer for solar cells,10,11 and active layer for light emitting diodes (LED),12,13 etc. The hydrogenated amorphous carbon films can be prepared by various techniques, such as plasma enhanced chemical vapor deposition (PECVD),14 pulsed laser deposition,15 ion beam assisted deposition,16 sputtering,17 Contributing Editor: Mauricio Terrones Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2016.522
and filtered cathodic vacuum arc.18 However, PECVD is the most suitable and widely used technique, which enables the growth of a-C:H films on a variety of substrates, and in a wide temperature range, especially at room temperature. Moreover, PECVD also produces the uniform deposition of a-C:H films over large area.19 To our knowledge, the effect of deposition parameter such as substrate temperature, gas flow, deposition pressure on the structural and opt
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