Ellipsometric analysis and optical absorption characterization of nano-crystalline diamond film

A nano-crystalline diamond (NCD) film with a smooth surface was successfully deposited on silicon by a hot filament chemical vapor deposition (HFCVD) method. Scanning electron microscopy (SEM), atomic force microscopy (AFM), RAMAN scattering spectra, as well as spectroscopic ellipsometry were employed to characterize the as-grown film. By fitting the spectroscopic ellipsometric data in the energy range of 0.75–1.50 eV with a three-layer model, Si∣diamond+non-diamond∣diamond+ non-diamond+void∣air, the optical constants are obtained. The refractive index of the NCD film varies little from 2.361 to 2.366 and the extinction coefficient is of the order of 10−2. According to the optical transmittance and absorption coefficient in the wavelength range from 200 to 1 100 nm, the optical gap of the film is estimated to be 4.3 eV by a direct optical transition mechanics.