Photoluminescence of bulk Si-Ge single crystals

Single crystals of Si-Ge alloy in the composition range from 0 to 50 at.%Si were grown with traveling solvent method. The compositions of the above crystals were shown to be uniform with EPMA measurement. The band gap energy of the crystals increased linearly in the range from 0 to about 15 at.%Si and varied gradually above 15 at.%Si. In order to determine the dependence of the symmetry of conduction band minimum on Si composition, we measured photoluminescence spectrum under uniaxial stress along < 111 > direction considering the difference of symmetry of conduction band minimum in Ge and Si. The dependence of peak energy of excitonic no-phonon line on uniaxial stress along < 111 > direction changed at about 15 at.%Si. From these results, it was confirmed that conduction band minimum was on Ge-like L points (< 111 >) at composition up to 15 at.%Si and on Si-like near X points (bottom of Delta) (< 100 >) above 15 at.%Si.