Spectroscopic ellipsometry study of non-hydrogenated fully amorphous silicon films deposited by room-temperature radio-frequency magnetron sputtering on glass: Influence of the argon pressure

Abstract

The complex dielectric functions of unhydrogenated amorphous silicon (a-Si) thin films, grown by the radio-frequency magnetron-sputtering (RFMS) technique, at room temperature, upon glass substrates, have been accurately determined by using ex-situ variable-angle spectroscopic ellipsometry, in the photon energy range from 0.73 to 4.96 eV (i.e. 1700 to 250 nm). Mass density of sputter-deposited amorphous silicon films was changed by a simple argon-working-gas pressure control: higher Ar gas pressure results in reduced film mass density, or increased porosity. The optical response of the hydrogen-less amorphous silicon films under study can be successfully parameterized employing a single, Kramers-Kronig (K-K)-consistent Cody-Lorentz (CL) oscillator dispersion model; the Urbach absorption tail included in the CL model, is certainly needed in the present case of hydrogen-free sputtered a-Si films. It has been unambiguously demonstrated that the obtained values of CL-model parameters are reasonably correlated with the particular argon-gas sputtering pressure utilized for each deposition. The behavior of these best-fit CL-model parameters with varying argon pressure from 0.13Pa up to 4.4Pa, can be clearly understood in terms of the effect of the existing micro-voids, within the as-deposited a-Si film material.