CHARACTERIZATION OF AMORPHOUS HYDROGENATED CARBON USING SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Amorphous hydrogenated carbon films deposited from a radio frequency (rf) plasma discharge were characterized with respect to their local bonding configurations and resulting electrooptical properties. Films deposited at substrate temperatures of 66–256 °C were examined with interferometry, ellipsometry, infrared spectroscopy, spectrophotometry, and electron spin resonance. The carbon bonding configurations and hydrogen content were subsequently measured with solid-state nuclear magnetic resonance (NMR). Observation of carbon-13 allowed for quantitative determination of the ratios of sp2:sp3 coordinated carbon and hydrogenated to non-hydrogenated carbon. It was found that with increasing deposition temperature, the energy gap decreased from 2.6 to 0.9 eV. The hydrogen content was constant between 16 and 23 at. % in these films. The sp2 fraction varied between 48 and 61% of total carbon but showed no trend as a function of deposition temperature. It is concluded that changes in hydrogen content or changes in average sp2 carbon content are not necessary to vary the electronic band structure of this amorphous semiconductor. The density of the material dramatically increased as a function of increasing deposition temperature, and it is suggested that the film density contributes to controlling the energy gap of these films. © 1990, American Chemical Society. All rights reserved.