Raman spectra of wurtzite- and zinc-blende-type ZnS single crystals were excited by a He-Ne laser (6328 Å) and an argon-ion laser (4880 Å and 5145 Å). All the Raman-active long-wavelength phonon frequencies were determined. These are (i) for the cubic modification, TO=276 ${\mathrm{cm}}^{-1\mathrm{}}$ and LO=351 ${\mathrm{cm}}^{-1\mathrm{}}$; and (ii) for the hexagonal modification, $E_2=72\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $E_2=286\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A_1\left(\mathrm{TO}\right)=E_1\left(\mathrm{TO}\right)=273\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, and $A_1\left(\mathrm{LO}\right)=E_1\left(\mathrm{LO}\right)=351\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The lowest-frequency $E_2$ mode of the mixed crystal system ${\mathrm{Cd}}_x{\mathrm{Zn}}_{1-x}\mathrm{S}$ was studied as a function of $x$, and was found to vary monotonically. The intensity ratio of the LO to the TO band seems to be dependent on the wavelength of the exciting radiation.

• Received 26 February 1968

DOI:https://doi.org/10.1103/PhysRev.171.931