The effects of surface characteristics on the visible and uv optical properties of CVD amorphous silicon films

Abstract

Silicon films were deposited by the pyrolytic decomposition of silane onto fused quartz substrates held at various temperatures in the range 550 to 800°C. The films are amorphous when prepared below a substrate temperature T s of 650 to 700°C. Scanning electron micrographs indicated that surface roughness increased with increasing T s. Optical properties were determined from near-normal specular reflectance and transmittance measurements in the energy range 0.5 to 14 eV. Diffuse reflectance measurements in the energy range 0.5 to 5.5 eV permitted the determination of the hemispherical reflectance. These measurements indicated that the CVD amorphous silicon films significantly scattered photons having energies above 2 eV. In addition, the uv measurements indicated the presence of silicon dioxide layers which was confirmed by specular reflectance measurements of samples annealed in air. The presence of scattering through surface roughness and the influence of oxide layers must be taken into account carefully when optical measurements above 2 eV are made the basis for a subsequent Kramers-Kronig analysis. Theoretical conclusions based on the results of such an analysis deserve confidence only if the surface roughness and oxide layers do not detectably affect the specularity of the optical measurements.