The influence of the film-substrate interface on the defect density and other properties of sputter-deposited amorphous hydrogenated silicon

The properties of sputter-deposited amorphous hydrogenated silicon have been found to vary considerably as a function of the film thickness for d<1 μm. This behavior can be interpreted as follows. The defect density decreases exponentially from 2×10¹⁷ cm^-3 at the substrate interface to values below 10¹⁶ cm^-3 in the bulk. A corresponding change in the Urbach energy E₀ indicates that structural inhomogeneities are the reason for the change of the density of states. As a consequence, the ημτ product drops by four orders of magnitude from 1 to 0.01 μm. With electron spin resonance measurements, additional defects that are directly located at the interface are detected. These additional defects might be caused by the creation of a-Si dangling bond-like defects on the surface of the SiO ₂ substrate due to the sputter process