Model calculations on the influence of dangling bonds on the optical properties of amorphous silicon films

The spectra of the optical constants of amorphous silicon films in the range 0.04hv5.6 eV, especially the very large infrared refractive indices obtained with high deposition rates, are fitted by the classical oscillator model. The oscillators considered are the three strongest single-crystal oscillators and an additional oscillator the existence of which can be ascribed either to dangling bonds in the microcrystal model or to an average non-covalent share of the bonds in the random network model. The sum of the four oscillator strengths is nearly independent of the degree of amorphousness. The calculated oscillator strength of the additional oscillator is proportional to the measured concentration of unpaired spins. The energy states of this oscillator in the E(k) diagram are placed along the axis Γ-L, and are parallel to the edges of the valence and conduction bands at a distance of 0.7±0.1 eV from the valence band.