Spectroscopic ellipsometry study of the relaxation state of amorphous silicon

Spectroscopic ellipsometry in the spectral range 0.25-0.9 mum was used to characterize the relaxation state of amorphous silicon. The thermodynamic state was changed either by thermal treatment of ion implanted amorphous silicon (leading to completely relaxed samples) or by further low dose ion implantation of the thermally relaxed material (leading to partially unrelaxed samples). The complex refractive index was calculated by fitting the ellipsometric functions tan psi and cos DELTA with a two-layer model and using for the amorphous silicon layer Forouhi dispersion relations, the most suitable for amorphous solids. A monotonic variation of both the real and imaginary parts of the refractive index between the curves of the fully relaxed and the fully unrelaxed samples was found. A strong correlation between the electronic structure as probed by optical measurements and topological short-range order was also revealed