Theoretical study of Raman modes in high-pressure phases of Si, Ge, and Sn

Results of an ab initio investigation of the pressure dependence of the Raman-active phonon modes in the {β}-Sn phase of Si, Ge, and Sn and the hexagonal-close-packed phase of Si are presented. The calculations are in very good agreement with experimental measurements. Both measurements and calculations show that the {β}-Sn-structure LO mode has a different pressure dependence for Ge than for Si. This difference between Si and Ge is discussed, and an explanation in terms of d electrons is given.