Electroreflectance spectroscopy of strainedSi1−xGexlayers on silicon

Electroreflectance spectroscopy was used to measure the critical point energies in strained ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ layers on Si in the energy region from 3 to 6 eV. Observed were the transitions $E_1{,E}_1+{\Delta }_1{,E}_0^{\prime }{,E}_0{,E}_0+{\Delta }_0{,E}_2{\mathrm{}\left(X\right),E}_2\left(\Sigma \right),$ and $E_1^{\prime }$ for germanium concentrations ranging from 12.5% to 28.1% at sample temperatures between 10 and 300 K. The transitions $E_1+{\Delta }_1{,E}_0{,E}_0+{\Delta }_0{,E}_2\left(\Sigma \right),$ and $E_1^{\prime }$ and their temperature dependence have not been reported before in strained ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ layers. Calculations of the strain shifts based on deformation potential theory are in good agreement with the experimental shifts of the $E_0$ transition, while deviations occur for the $E_1$ transition.