• PDF / 114,695 Bytes
• 4 Pages / 612 x 792 pts (letter) Page_size
• 82 Downloads / 300 Views

DOWNLOAD

REPORT

---

Wei Li and Tianfu Ma National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093

Zhifeng Li National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, CAS, Shanghai 200083, China

Li Wang and Kunji Chen National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, CAS, Shanghai 200083, China

Hydrogenated amorphous carbon thin films were prepared by using organic hydrocarbon source, xylene (C8H10), in a plasma enhanced chemical vapor deposition (PECVD) system. In contrast to a single broad PL peak from methane (CH4)-based hydrogenated amorphous carbon films, a new PL feature was observed from xylene-based a–C:H films in the blue-green light region. It was found that the aromatic structures were enhanced in xylene-based a–C:H films deposited at high radio frequency power, which may result in the existence of luminescence centers in the carbon films and induce the appearance of a new PL peak.

Recently, the study on hydrogenated amorphous carbon (a–C:H) films has become one of the hot topics in the research field of material physics both because of their interesting physical properties and their potential applications in various opto-electronic devices.1,2 It is well known that the polymerlike carbon (PLC) films can emit photoluminescence (PL) at room temperature in the red-green light region and it is expected to develop them as electro-luminescent materials.3 Generally, PLC films were prepared by using methane (CH4) as the carbon source in the plasma enhanced chemical vapor deposition (PECVD) system and many articles have been published on the microstructures and photoluminescence mechanism in those films.4–7 It was found that the PL spectra showed a single broad peak with its full width at halfmaximum (FWHM) about 0.5 eV. No clear relationship between the PL peak energy and the optical Tauc gap was found and the luminescence is a much faster and weaker temperature dependence.6 It also was reported that the PL peak shifts to the lower energy and the bandwidth was reduced when decreasing the excitation en-

a)

Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 2, Feb 2001

http://journals.cambridge.org

Downloaded: 31 Mar 2015

ergy; when the excitation energy was above a certain value, the PL shape was almost unchanged.5 The modified band tail luminescent model of hydrogenated amorphous Si (a–Si:H) was used to describe the PL behavior in a–C:H films.8 In the present stage, the PL mechanism for PLC films is still unclear and to use a carbon source other than methane to further improve the PL efficiency also is an open question.9 Xylene (C8H10) is in liquid state at room temperature and the three kinds of formula for its molecular are shown in Fig. 1. It was reported that xylene molecular has the lower toxicity compared with benzene, it also is less fragmented of its aromatic rings in plasma and it can prevent the formation of microstructures in carbon films.10 Actual