A study of direct optical transitions in silicon single crystals based on transmission spectra

The transmission spectrum of single-crystal silicon in the range of 2.75–3.25 eV has been obtained experimentally. An empirical formula is proposed to describe the spectral dependence of the optical density. The energy of the direct transition at the saddle point is found to be $E(\Gamma_{15})-E(\Gamma_{25'})$ = 3.43 eV. Analysis of the spectral dependence showed that the observed absorption corresponds to direct transitions to the van Hove singularity $M_1$ of the conduction band.