RAMAN SCATTERING IN ULTRA HEAVILY DOPED Si AND Ge: THE DEPENDENCE ON FREE CARRIER AND SUBSTITUTIONAL DOPANT DENSITIES.

The authors present the results of a systematic study of phonon softening due to free electrons and holes in extremely heavily doped Si and Ge. Metastable concentrations of Bi, Sb, As, P, Al and B were implanted and pulsed laser annealed (ruby or XeCl) to produce substitutional concentrations up to 4 multiplied by 10**2**1 cm** minus **3. The authors find softening of the zone center optic phonon of as much as approximately 5% in p-type Ge, approximately 5. 4% in p-type Si, and 2% in n-type Si. The shifts are explained by phonon coupling to single particle electronic excitations. In addition they discuss the density dependence of the Raman-active vibrational local modes of P and Al in Ge and of B in Si which they demonstrate can provide a convenient measure of substitutional concentrations of these low mass dopants.