Bound state energy and line width due to the resonant interaction between optical phonon and electronic transitions in degenerate silicon

For free carrier concentration larger than 10²⁰ cm^-3 donors or 10¹⁹ cm^-3 acceptors, silicon is degenerate and electronic interconduction band or intervalence band transitions are possible for energies of the order of the optical phonon energy. Light scattering experiments show that the coupling of these two elementary excitations leads to a bound state broadened and shifted to lower energy. Analysis of the variation of the line width and the shift of the band as a function of the impurity concentration is presented. Results obtained on silicon heavily doped by ion implantation followed by laser annealing show even more pronounced shift related to band structure and phonon dispersion modifications due to the very high dopant concentration.