Experimental evidence for an inhomogeneous surface dangling bond limited growth mechanism in a-Si:H

Abstract The growth mechanism of hydrogenated amorphous silicon (a-Si:H) deposited by radio frequency (rf) plasma enhanced chemical vapour deposition (PECVD) has been studied by in situ scanning tunnelling microscopy (STM) at several stages during growth. The data showed that the surface has an island-like structure. The radially averaged Fourier transform of the topography reveals, quantitatively, how feature density scales with feature size. This yields a Fourier index of between 1.1 and 1.4 for the a-Si:H surface, which differs from the value of 4 which would be expected for a surface growing through surface diffusion alone. We suggest, based on chemical arguments, that growth occurs by the diffusion of SiH 3 radicals over the hydrogen terminated a-Si:H surface and their subsequent attachment to dangling bonds. We suggest that these dangling bonds preferentially form at kink-like and step-like surface sites, where hydrogen is sterically hindered. A simple computer simulation of this mechanism reveals that an island-like topography is indeed produced by this mechanism with a Fourier index of ∼1.55.