Piezoreflectance Studies of GaP and Ge

The piezoreflectance spectra of GaP and Ge are studied at 300 K in the spectral range 1.9 to 5.3 eV. In GaP the structure at 2.7 eV is confirmed to arise from a transition from a p-like state to an s-like state. The spin-orbit splitting of the p-like state is obtained as 0.05 eV. From the dependence of the reflectivity change on polarization and stress direction, the E 1 structure at 3.7 eV is shown to be a superposition of two singularities of different types. The energies of the E 0 ' and E 2 edges agree with those obtained by electroreflectance measurements, but the location of the E 2 edge in k -space conflicts with the previous assignment. In Ge, the E 0 ' edge is shown to be located along a [001] direction. The type of the E 1 edge and the locations of the E 2 edge in k -space are also discussed.