Surface roughness evolution of a-Si:H growth and its relation to the growth mechanism

Abstract
The post-initial growth dynamic scaling exponent β, which describes the surface roughness evolution in time, is determined for a-Si:H growth using in situ single wavelength (632.8 nm) rotating compensator ellipsometry. β is measured as function of the substrate temperature for three different growth rates 2, 5 and 22 Ås-1 under conditions where SiH3 dominantly contributes to growth. β (≤ 0.5) decreases with increasing substrate temperature and does not strongly depend on the growth rate within the range of growth rates. A roughness evolution model is proposed, based upon a random generation of active growth sites and a subsequent site dependent surface diffusion process. The measured β temperature dependence can be simulated with an activated site hopping activation energy of about 1.0 eV. This activation energy is much higher than what would be expected from a model based upon the diffusion of physisorbed silyl SiH3 radical and suggests therefore another mechanism which is responsible for the surface smoothening during a-Si:H growth.