Characterization of chemical-vapor-deposited amorphous-silicon films

We have studied post-hydrogenation characteristics and photo-absorption characteristics of amorphous-silicon films thermally deposited from disilane at 500°C. There is a critical post-hydrogenation temperature of about 400°C, below which both the density of hydrogen (deuterium) atoms on the surface and the activation energy of their diffusion constants are constant. Post-hydrogenation drastically enhances the decrease of the photo-absorption coefficient for photon energies less than the optical bandgap. The optimum density of hydrogen atoms introduced by post-hydrogenation was between 3 at% and 3.5 at%. The Urbach tail slope Eq was 42 meV, i.e., about 8 meV lower than the typical value of the film deposited by plasma enhanced chemical vapor deposition (PECVD) method.