Analysis of specular and textured SnO2:F films by high speed four-parameter Stokes vector spectroscopy

Abstract

A rotating-compensator multichannel ellipsometer has been applied to measure the unnormalized Stokes vector that describes the polarization state of light reflected from specular and textured SnO2:F transparent conducting films on glass substrates. This four parameter spectroscopy yields the ellipsometric angles (ψ, Δ), the reflectance R, and the degree of polarization p, with a potential repetition time of 32 ms for all four 100 point spectra from 1.5 to 3.75 eV. The rotating-compensator design permits high accuracy evaluation of Δ over its full range (−180°<Δ⩽180°), even in the presence of random depolarization. This allows accurate analyses of the microscopic structure and optical properties of the SnO2:F films, based on fits to (ψ, Δ) using an ideal (specular) multilayer model. Differences between the reflectance spectrum predicted from the ideal model and that from experiment can be understood by including light scattering at the film surface due to texture (i.e., macroscopic roughness on the scale of the wavelength) in the model. The macroscopic roughness layer distribution can be extracted based on fits to R. The information obtained optically from {(ψ, Δ), R} is corroborated by direct structural measurements. Finally, we find that the spectra in p for both the specular and textured SnO2:F films exhibit oscillations that are attributed to sample nonuniformities over the beam area, with possible contributions from other sources. The similarity of p for both samples, along with the consistency of the (ψ, Δ) analysis results for the textured SnO2:F film, suggest that the scattering generated by the texture does not distort the information accessible through the polarized component of the reflected beam.