First-order raman effect in wurtzite-type crystals

First-order Raman scattering from BeO, ZnO, ZnS, and CdS, all having the wurtzite structure (C6v), 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 E2 mode was resolved from the transverse modes for the first time. The assignments of the E2 modes in ZnS differ from previous investigations. From absolute intensity measurements, electro-optic coefficients for BeO, ZnO, and CdS were determined.