OPTICAL ANISOTROPY INVESTIGATION IN ZN1-XCDXSE ZNSE MULTIQUANTUM WELLS BY 2-PHOTON SPECTROSCOPY/

The tight polarization dependence of two-photon absorption (TPA) near half the band gap has been experimentally investigated in Zn1-xCdxSe/Z nSe strained-layer multi-quantum wells. A detailed analysis of their T PA photoluminescence spectra, measured for two different polarization configurations of the exciting laser beam (perpendicular and parallel to the QW growth axis z), permitted us to sensitively probe the excito n anisotropy in quasi-bidimensional (Q2D) heterostructures. Fundamenta l and excited exciton states of different symmetry have been selective ly detected by exploiting the strong anisotropic selection rules for T PA processes. In particular, the polarization along the z axis allowed us to obtain the first clear experimental evidence of higher-order li ght-hole excitons. Our experimental results are in good agreement with theoretical predictions of an analytical model of TPA in Q2D exciton systems, demonstrating the usefulness of a simplified approach for the case of photon energies close to half the band gap.