Piezo-optical Evidence forΛTransitions at the 3.4-eV Optical Structure of Silicon

We report the effects of large uniaxial stresses, which produce splittings and shifts large compared to the spin-orbit interaction, along the [001] and [111] direction on the wavelength-modulated reflectivity spectrum of Si in the region around 3.4 eV. Our results are interpreted in terms of both interband and intraband splittings of the orbital bands and indicate conclusively that the optical structure corresponding to the main peak in reflectivity around 3.4 eV is due to ${\Lambda }_3-{\Lambda }_1$ (or $L_{3^{\prime }}-L_1$) transitions.