Electroreflectance spectroscopy of strained Si1-xGex layers on silicon

Electroreflectance spectroscopy was used to measure the critical point energies in strained Si1-xGex layers on Si in the energy region from 3 to 6 eV. Observed were the transitions E-1,E-1+Delta(1),E-0',E-0,E-0 +Delta(0),E-2(X),E-2(Sigma), and E-1' 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(Sigma), and E-1' and their temperature dependence have not been reported before in strained Si1-xGex 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.