First-Order Raman Effect in Wurtzite-Type Crystals

First-order Raman scattering from BeO, ZnO, ZnS, and CdS, all having the wurtzite structure (${C}_{6v}$), has been investigated. A discussion of the effects of the competition between the long-range electrostatic forces and the short-range forces due to anisotropy in the interatomic force constants on the vibrational spectrum has been included. A series of scattering diagrams are presented showing the geometrical arrangements necessary to observe all the $k=0$ phonons for this type of crystal structure. In BeO the ${E}_{2}$ mode was resolved from the transverse modes for the first time. The assignments of the ${E}_{2}$ modes in ZnS differ from previous investigations. From absolute intensity measurements, electro-optic coefficients for BeO, ZnO, and CdS were determined.