We report values of pseudodielectric functions $〈\epsilon 〉=〈{\epsilon }_1〉+i〈{\epsilon }_2〉$ measured by spectroscopic ellipsometry and refractive indices $\tilde{n}=n+ik$, reflectivities $R$, and absorption coefficients $\alpha$ calculated from these data. Rather than correct ellipsometric results for the presence of overlayers, we have removed these layers as far as possible using the real-time capability of the spectroscopic ellipsometer to assess surface quality during cleaning. Our results are compared with previous data. In general, there is good agreement among optical parameters measured on smooth, clean, and undamaged samples maintained in an inert atmosphere regardless of the technique used to obtain the data. Differences among our data and previous results can generally be understood in terms of inadequate sample preparation, although results obtained by Kramers-Kronig analysis of reflectance measurements often show effects due to improper extrapolations. The present results illustrate the importance of proper sample preparation and of the capability of separately determining both ${\epsilon }_1$ and ${\epsilon }_2$ in optical measurements.

• Received 6 July 1982

DOI:https://doi.org/10.1103/PhysRevB.27.985