RESONANT RAMAN-SCATTERING AND EXCITONIC POLARITON STATES IN CUGAS2

Scattering processes and the relevant intermediate state for intense R aman lines appearing in the exciton region spectrum of CuGaS2 under 47 65 angstrom excitation of an Ar+ laser are discussed from measured int ensity changes of the lines with temperature as well as photon energy of excitation. Experimental results are consistent with the previous i nterpretation that the line at 2.504 eV corresponds to a three-phonon Raman scattering in resonance with the upper-branch excitonic polarito n (UBP) state. The line at 2.509 eV is thought to correspond to a two- phonon Raman scattering in resonance with the UBP state.