Raman Scattering and Two-Phonon Infrared Transmission Spectra of Cu(AlxGa1-x)S2 Crystals.

First- and second-order Raman scattering and two-phonon infrared (IR) transmission measurement results for Cu(Alx Ga1-x )S2 single crystals have been examined as a function of x. It is apparent that the highest frequency B2 and E modes at the zone center exhibit two-mode(persistence)-type behavior. The appearance of the two-mode-type behavior in a ternary alloy system is shown to be explainable by theoretical consideration based on a modified model of the type judging criterion. In addition, some of the two-phonon IR absorption bands and second-order Raman peaks are found to be due to phonons located at zone-boundary points. Compositional dependence of the A1(W1) mode Raman line shape and the appearance of a cross-coupled phonon between the two modes indicate that the clustering effect is essentially suppressed in this alloy system.