X-ray absorption of Si-C-N thin films: A comparison between crystalline and amorphous phases

X-ray absorption near edge structure (XANES) spectra of crystalline (c)- and amorphous (a)-Si-C-N thin films were measured at the C, N, and Si K edge using the fluorescence and sample drain current modes. A sharp peak similar to the C 1s core exciton in chemical vapor deposition diamond is observed, which can be assigned to the transition from the C 1s to sp³ hybridized states in c-Si-C-N. The C K edge XANES spectrum of a-Si-C-N contains a relatively large 1s→π^* peak, implying that carbon atoms in the a-Si-C-N film are bonded largely in graphite-like sp² configurations. A shift of the a-Si-C-N π^* peak towards the lower energy by ∼0.3 eV relative to that of c-Si-C-N is observed, which can be attributed to a higher degree of disorder-induced localization of excited electrons. Both a- and c-Si-C-N N K-edge XANES spectra resemble that of α-Si₃N₄. The Si K-edge absorption spectra of the Si-C-N thin films indicate a proportional combination of local Si-N and Si-C bonds. The increase of the binding energies of excited electrons and the broadening of the spectral features by structural disorder are also observed in the Si K-edge XANES spectrum of the a-Si-C-N film.