Publication

Abstract : Nanocrystalline silicon carbide ~SiC! thin films were deposited by plasma enhanced chemical vapordeposition technique at different deposition temperatures (Td) ranging from 80 to 575 °C and different gas flow ratios ~GFRs!. While diethylsilane was used as the source for the preparation ofSiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. Theeffects of Td , GFR and dilution gases on the structural and optical properties of these films wereinvestigated using high resolution transmission electron microscope ~HRTEM!, micro-Raman,Fourier transform infrared ~FTIR! and ultraviolet-visible optical absorption techniques. Detailedanalysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in theamorphous matrix of the films deposited at a temperature of 300 °C. The degree of crystallizationincreases with increasing Td and the crystalline fraction (f c) is 65%62.2% at 575 °C. The f c is thehighest for the films deposited with hydrogen dilution in comparison with the films deposited withargon and helium at the same Td . The Raman spectra also confirm the occurrence of crystallizationin these films. The HRTEM measurements confirm the existence of nanocrystallites in theamorphous matrix with a wide variation in the crystallite size from 2 to 10 nm. These results are inreasonable agreement with the FTIR and the micro-Raman analysis. The variation of refractiveindex ~n! with Td is found to be quite consistent with the structural evolution of these films. Thefilms deposited with high dilution of H2 have large band gap (Eg) and these values vary from 2.6to 4.47 eV as Td is increased from 80 to 575 °C. The size dependent shift in the Eg value has alsobeen investigated using effective mass approximation. Thus, the observed large band gap isattributed to the presence of nanocrystallites in the films.