The change of photoluminescence characteristics of amorphous carbon films due to hydrogen dilution

Abstract A series of hydrogenated amorphous carbon films were prepared using the hydrogen dilution method in a plasma enhanced chemical vapor deposition system. The luminescence characteristics were studied as a function of hydrogen dilution ratio. A broad PL band centered at 2.45 eV was found in the sample without hydrogen dilution. With increasing hydrogen dilution ratio, both the optical band gap and the photoluminescence peak were shifted to high energy as a consequent of the size decrease of π bonding states of the sp 2 hybridized carbon phases. A change of the PL characteristics was found on further increasing the hydrogen dilution ratio to 1.5. Besides the PL band around 2.45 eV, a new PL band at 3.05 eV appeared as the excitation photon energy exceeded 3.31 eV. Based on the measurements of structural and bonding configurations, the PL band can be attributed to the radiative recombination of geminate electron–hole pairs in small sp 2 clusters containing CC and C–H units.