Optical transitions in strained Si1−yCy layers on Si(001)

The effect of the carbon content on the optical transitions of Si1−yCy layers grown pseudomorphically on Si(001) substrates was investigated by spectroscopic ellipsometry and electroreflectance spectroscopy for 0≤y≤0.012 in the energy range between 3 and 5 eV. The ellipsometry data show a decrease of the slope of the dielectric function near the critical points and a tendency of a critical point shift with increasing carbon content. This shift was analyzed by measuring and fitting electroreflectance spectra at 80 K, resulting in a weak and linear dependence on the carbon content at all transitions. The E1 critical point energy increases with an increasing carbon content while the E2 energy decreases, both at a rate of about 30 meV/%[C]. The E’0 transition decreases at a smaller rate of about 20 meV/%[C]. The results are discussed in the light of previous discussions and a simple estimate based on silicon deformation potentials.

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