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 0.290.05 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 15 and 5 which can produce interference. In the limit of zero stress, a ratio of the intensities of the doublet components =5.70.5 is determined. The experiment allows also a direct measurement of the deformation potentials, giving results in very good agreement with pseudopotential calculations. © 1978 The American Physical Society.