Optical properties of diamond-like carbon thin films deposited by DC-PECVD
Keywords:Diamond like carbon, DC-PECVD, Optical properties, Photoluminescence, Amorphous carbon,
Diamond-like carbon (DLC) thin films were deposited at different substrate temperatures using methane gas in DC-PECVD at 1x10-1 Torr. From the light
transmission using UV-VIS spectroscopy it was found that the optical transition had changed from allowed indirect transition to forbidden direct
transition as the substrate temperature increased. The photoluminescence study has shown that the recombination centre occurred at 1.738 eV. The
observation in the present work shows that the Urbach energy decreases with increasing substrate temperature provides evidence that such films have a
narrowed band tail. This decrease in Urbach energy is due to a more ordered structure with lower hydrogen concentration and larger cluster by the
increase in the degree of cross-linking of the C-C network. Distorted cluster which contribute to the broadening of the band tail may also contribute to the
PL peak width. As the substrate temperature increases, the cluster size in the tetrahedral hydrogenated amorphous carbon (ta-C:H) increases, resulting in
smaller band gap and the structure is more ordered as the decrease in Urbach energy, give the decrease in PL peak energy.
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