No abstract

No abstract

Undoped and boron-doped a-Si 1−x C x :H, for x ≈ 0.5, films have been prepared by means of plasma-enhanced chemical-vapour deposition using methyltrichlorosilane.The optical absorption spectra of these films demonstrate three characteristic peaks at about 1.6, 2.0 and 2.5 eV consistent with other experimental measurements. To explain the observed peculiarities of the spectra, the atomic and electronic structures of a-SiC have been investigated using both molecular dynamics simulations based on an empirical potential and the recursion method. The results of the calculations show that fivecoordinated (T 5 ) atoms (floating-bond atoms), anomalous four-coordinated (T 4a ) sites (weak-bond atoms), three-coordinated (T 3 ) defects (dangling-bond atoms) and normal four-coordinated (T 4n ) atoms which are nearest neighbours of T 3 , T 4a or T 5 atoms give rise to three gap peaks. It was established that three peaks in the low-energy region of the optical absorption spectra are due to the electronic transitions: the valence band → the empty gap peak and two occupied gap peaks → the conduction band. Boron doping effects upon the optical spectra was not revealed.

No abstract

The character of relaxation of atoms around a vacancy in cubic silicon carbide is determined with the help of the empirical potential of Tersoff. The recursion method of Haydock and Nex is applied to calculate the density of states derived from atoms situated around the defect. The outward relaxation of the lattice surrounding a empty site is established. The lattice relaxation results in the shift of gap states toward the conduction band. Vacancy levels of carbon at 0.5 eV and silicon at 0.45 and 1.98 eV are revealed in the band gap. The obtained results are compared with the experimental ones and with the data of other calculations. The work shows the importance of taking into account the lattice relaxation in examining vacancy states in semiconducting compounds.