Raman study of the interaction between localized vibrations and electronic excitations in boron-doped silicon

The Raman spectrum of localized boron vibrations in heavily doped silicon is studied as a function of exciting laser frequency. The resulting line shapes are markedly asymmetric and show a pronounced dependence on the frequency of the exciting laser line. These results are explained as Fano-type interference between a continuum of Raman-active electronic excitations due to the free holes and the discrete localized-mode vibronic scattering. This effect is compared to the influence of free holes in the Raman spectrum of the zone-center optical phonon. From this comparison, conclusions as to the effect of the boron impurities on the electronic band structure are drawn and some deformation potentials associated with the localized vibrations are estimated.