Graduate Thesis Or Dissertation
 

Diamond-like carbon films for electroluminescent applications

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  • White electroluminescence (EL) was observed for the first time from diamond-like carbon (DLC) films at room temperature. Electroluminescence was observed by the application of ac voltages in excess of 200 V to a metal-insulator- semiconductor (i.e. DLC)-insulator-metal (MISIM) device structure. For EL applications, three types of the DLC films were prepared by plasma-enhanced chemical vapor deposition (PECVD) using a commercially available reactor (Semi-Group System 1000). The plasma excitation frequency was either 13.56 MHz or 100 kHz and the system has a capacitively coupled, parallel plate configuration in which the substrate electrode was either grounded or powered. DLC films were deposited using a source gas mixture of 10 % methane diluted in helium. The critical temperature for obtaining a DLC deposition was found to be a function of the electrode spacing. Using the conventional electrode spacing of 25 mm, it was not possible to deposit DLC films above 200°C. When the electrode spacing was decreased to 14.5 mm, however, DLC films were obtained at substrate temperatures up to 300°C. The optical bandgap of the DLC films could be varied from 2.2-3.0 eV using typical process deposition parameters. In contrast to other reports, the optical bandgap did not strongly depend on the deposition temperature, rf power, or pressure. A reduction in optical bandgap of thermally annealed DLC films was observed, compared to that of the asdeposited DLC films. The films also exhibited photoluminescence (PL) which was observed at room temperature. The EL and the PL spectra were compared. The PL peak energy shifts were observed by decreasing measuring temperature and by changing the deposition power. Periodic oscillations in the PL spectrum were observed when a low optical pumping energy was used; these oscillations were attributed to C-H wagging modes.
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