Complex dielectric function of biaxial tensile strained silicon by spectroscopic ellipsometry

The complex dielectric function of biaxial tensile strained Si grown on a fully relaxed Si_0.81Ge_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 E₀^′∕E₁ gap region, whereas the CP’s in the E₂ region were relatively unaffected. These results compare favorably to previous reports for uniaxially compressed stressed silicon. In particular, the experimentally observed splitting of the E₁ gap— E₁(1)=3.310  eV and E₁(2)=3.437  eV —was in reasonable agreement with calculated expectations— E₁(1)=3.304  eV and E₁(2)=3.395  eV —using previously reported Si deformation potentials.