Complex dielectric function of biaxial tensile strained silicon by spectroscopic ellipsometry

Abstract

The complex dielectric function of biaxial tensile strained Si grown on a fully relaxed ${\mathrm{Si}}_{0.81}{\mathrm{Ge}}_{0.19}$ virtual substrate was obtained from spectroscopic ellipsometry measurement in the 2.5--5-eV energy range. Standard critical point (CP) line shapes were fit to numerically obtained second-derivative spectra to extract interband CP parameters. It is shown that the biaxial tensile strain increased the number of ellipsometrically observable CP's from two to three in the ${E}_{0}^{\ensuremath{'}}∕{E}_{1}$ gap region, whereas the CP's in the ${E}_{2}$ region were relatively unaffected. These results compare favorably to previous reports for uniaxially compressed stressed silicon. In particular, the experimentally observed splitting of the ${E}_{1}$ gap---${E}_{1}(1)=3.310\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and ${E}_{1}(2)=3.437\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$---was in reasonable agreement with calculated expectations---${E}_{1}(1)=3.304\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and ${E}_{1}(2)=3.395\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$---using previously reported Si deformation potentials.