Plausible interpretation of optical absorption spectra of a-SiC:H thin films

Boron-doped and undoped a-Si1−xCx:H, for x≈0.5, films were prepared by a plasma-enhanced-chemical-vapor-deposition from methyltrichlorosilane as the main precursor. Optical absorption spectra of these films demonstrate three characteristic peaks at ∼1.6, 2.0–2.2 and 2.5–2.8 eV in agreement with other experimental measurements. In order to account for the observed peculiarities of the spectra, the atomic and electronic structures of a-SiC were investigated using both molecular dynamics simulations based on Tersoff’s potential and the recursion method. The results of the model band structure calculations revealed three main peaks in the gap (∼2.45 eV), originated from homonuclear Si–Si bonds, five-fold (T5), anomalous four-fold (T4a), three-fold (T3) coordinated defects and normal four-fold (T4n) coordinated atoms which are the nearest neighbors of these defects. The optical absorption peaks are assumed to be formed as a consequence of electronic transitions between the valence band (VB), the three gap peaks and the conduction band (CB). Boron doping effects upon the optical spectra was not revealed.