We report the resonance of the first-order Raman scattering by phonons in pure and heavily doped n-type Ge for the region of the $E_1$ and $E_1$+${\Delta }_1$ gaps (1.8–2.7 eV) at room temperature. Our main observations are (i) a shift of about 50 meV for the peak in the resonance curve for pure Ge as compared with earlier measurements, (ii) a systematic red shift of the resonance curve for doped Ge with respect to the curve for pure Ge, and (iii) increased doping results in a substantial reduction of the resonance enhancement, which is almost suppressed in one of the heaviest-doped samples. The measured absolute scattering efficiencies have been analyzed based on analytical expressions for the susceptibility within a two-dimensional parabolic-band model of the critical points. The fit of the data with theory yields the two deformation potentials ‖$d_1$,$0^5$‖=31.30 eV and ‖$d_3$,$0^5$‖=46.9 eV. The calculated resonance strengths for the doped samples have to be reduced significantly in order to explain the observed ones. This can be understood semiquantitatively on the basis of the blocking of transitions near the L point by the free electrons.

• Received 5 November 1984

DOI:https://doi.org/10.1103/PhysRevB.31.3760