Growth mechanism of hydrogenated amorphous silicon studied by in situ scanning tunneling microscopy

In situ scanning tunneling microscopy has been used to study the evolution of the surface topography of the growing surface of hydrogenated amorphous silicon (a-Si:H) in order to understand its growth mechanism. The surface is found to possess an island-like structure and the island diameter is found to increase with increasing growth temperature. A Fourier analysis of the surface roughness has an exponent of i=1.17. A comparison of the roughness of films of different thickness gives a dynamic scaling exponent of β=0.28, but the films are not particularly self-affine in character. It is argued that the exponent i is not evidence of a viscous flow regime, but that nonstochastic growth of a random network occurs, caused by a preferential hydrogen abstraction at kink-like and step-like surface sites. A simple simulation of the topography is used to support this conclusion.