Uniaxially stressed silicon: Fine structure of the exciton and deformation potentials

The splitting of the indirect exciton in Si is measured, at the TO-phonon-assisted threshold, as a zero-stress extrapolation of the multiplet structure due to uniaxial stresses applied in the [001] direction. The validity of the method is warranted by a theoretical analysis of the exciton wave functions and energy levels under the combined influence of mass anisotropy and external perturbation. For the splitting, a value of 0.29±{}0.05 meV is found and compared with the latest theoretical estimate of the mass-anisotropy effect which includes coupling with the split-off valence band; the measured splitting, however, may include a contribution from exchange interaction. The intensities of the exciton components for moderately high stress are quite consistent with those calculated for an indirect transition mechanism involving only two intermediate states Γ₁₅ and Δ₅ which can produce interference. In the limit of zero stress, a ratio of the intensities of the doublet components η=5.7±0.5 is determined. The experiment allows also a direct measurement of the deformation potentials, giving results in very good agreement with pseudopotential calculations.