Brillouin study of acoustic phonon softening and optical absorption coefficients of ultraheavily doped n-Si

The self-energies of acoustic phonons in ion implanted and laser annealed ultraheavily doped n-type Si have been measured by Brillouin scattering. The corresponding softening of the elastic constants has been estimated from the observed phonon softening and compared it with theory. At high doping levels ($\text{N}{}_{\mathrm{e}}\text{≧ 10}{}^{21}\text{cm}{}^{-3}$) the effect of the increase in atomic mass on the phonon frequency is observed in the case of doping with As. From the increase in the linewidths of the Brillouin lines with doping, the optical absorption coefficients for $\text{λ = 5145}\text{A}\text{?}$ as a function of doping are determined.