Exciton resonance of hyper-Raman and hyper-Rayleigh scatterings in II–VI compounds

Abstract

Strong signals of both hyper-Raman scattering by optic phonons and hyper-Rayleigh scattering (SHG), the latter of which is forbidden by the usual selection rules, were found to emerge in two-photon resonance with excitation energy of the 2P excitons in a thin film sample of ZnSe on GaAs substrate. Both excitation spectra, which are found to be basically similar to each other, indicate an energy-splitting of the 2P excitons. As a result, it is found that the sample of 5 μm thickness suffer in-plane strains due to lattice misfit between ZnSe and GaAs, an order of which has been estimated thereby as ε ≈ 5 × 10 -4. A similar resonant hyper-Raman scattering was also found in a bulk sample of CdS, and is utilized for gaining into insight the microscopic origin of the phenomenon. On the basis of the results, it is discussed that the present phenomena, found for the first time in solids, would serve as novel spectroscopic methods for characterizing sample quality of II–VI compounds recently developed by state-of-the-art methods, through the strain-induced structure of the 2P excitons free from polariton effects.