Resonant Raman Scattering and Its Correlation to Exciton Luminescence in AgGaS2

Resonant Raman scattering and luminescence are studied for secondary emission in AgGaS2 using polarized excitation. At 8.6 K, a series of multiple phonon Raman lines are observed in addition to the ordinary luminescence bands due to free exciton, bound exciton and shallow donor states. The usual selection rule of optical transition is valid for the two radiation components in the vicinity of the band edge region. The intensities of both first order Raman and luminescence features are enhanced in the same energy region when the excitation energy is slightly higher than the free exciton energy. The resonance of this scattering from longitudinal optic E-phonons exhibits a temperature-dependent enhancement correlated with the thermal shift of the exciton gap and in the emission energies, especially of the free and bound excitons at low temperatures. The damping constants and relative strengths of the resonances at the luminescence states are determined and compared with those at the intrinsic exciton level.