Dielectric functions of strained silicon layers grown on very thick, relaxed Si1−xGex (x=0.115, 0.3, and 0.37) layers are presented. The effect of tetragonal biaxial strain to the dielectric function is observed to be large near the E1 gap region. We compare the strain-induced change in the dielectric function of silicon layers with that of SiGe layers and the elasto-optical (or piezo-optical) constants of silicon which were measured from bulk Si under uniaxial compressive stress.
We used room-temperature ellipsometry to study the quasidirect (no-phonon) transitions of disordered In& Ga P/graded GaP near crossover compositions (0.64~x~0 .75) for the I &, and X&, conductionband minima. Careful study of sample microstructures by transmission electron microscopy revealed no ordering. We identify the observed transitions at (I », -X&, ), (I »"-L&, ), and (I », -X3, ). The enhanced amplitude of the quasidirect transitions is attributed to band mixing between I and L or X points in k space. This observation is corroborated by low-temperature photoluminescence and time-decay experiments. A two-level anticrossing behavior of the I &, and X"gaps is observed in photoluminescence with
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