Abstract
The nature of the hydrogen bonds and their influence on film (micro/nano)structure has been investigated as a function of substrate temperature T-S (200-500 degrees C) in hydrogenated amorphous silicon carbide (a-SiC:H) thin films. These films were prepared by radio-frequency magnetron sputtering at a common pressure and high hydrogen dilution in the gas phase mixture (Ar + 80% H-2). Infrared absorption and Raman spectroscopy experiments have been carried out to characterize the (micro/nano)structure of different series as a function of T-S. The results of Fourier transform infrared spectroscopy indicate that all series are characterized by the presence of the low Si-H and C-H bond concentration and no absorption band at 2000 cm(-1) attributed to isolated monohydride Si-H can be detected, which suggests that the hydrogen is predominantly bonded as polyhydride groups (Si-H-2)(n), giving the band at 2090 cm(-1). The concentration of the Si-C bond and the crystalline fraction, which increase with increasing T-S, show an improvement in the crystallinity of the films. The influence of T-S on the growth of crystalline nanograins is studied by Raman spectroscopy. At temperatures T-S >= 200 degrees C, these films contain Si-C crystallites in addition to the Si nanocrystals distributed in the amorphous network. The Si crystallite size is unaffected by the increase of T-S but the size of graphitic domains is reduced and their distribution becomes more disordered. Results of Raman spectroscopy show also that the high values obtained for the line width of transverse acoustic TA-like band toward low frequencies justifies the deconvolution of infrared spectra taking into account the doublet (845 and 910 cm(-1)). The results of this paper therefore shed light on the origin of amorphous and nanocrystalline structure in the a-SiC:H thin films, which has been a subject of debate for decades.