Matrix Elements for the Indirect Piezoabsorption Coefficient in Silicon

Relative matrix elements are calculated for the absorption coefficient in the indirect-absorption-edgeregion for uniaxially stressed silicon. The calculations are for $〈100〉$, $〈110〉$, and $〈111〉$ stress, for all possible phonons, for all independent polarization directions of the light, and through all relevant intermediate states. The results are compared with experiments and interpreted to show that the deformation potential $b$ is negative and that several intermediate states must participate in the transition, resulting in interference effects.