Nonlinear Optical Properties of Semiconductor Nanowires

The orientation dependency of nonlinear optical effects, including the second-harmonic generation (SHG) and third-harmonic generation (THG), as well as two-photon luminescence, in semiconductor nanowires (NW) are described. The mismatch of dielectric constants between nanostructures and their environment governs the rise of optical nonlinearities causing SHG even in materials with a high symmetry crystal lattice that would not generate second harmonic in the bulk state. Due to the depolarization effects, the intensity of the optical electric field inside illuminated NWs depends dramatically on their orientation related to the exciting light polarization. As a result, rotation of the light polarization causes giant angular dependency of all the mentioned optical phenomena, with the maximum relative amplitude at the electric-field polarization oriented along the NWs. Simultaneous measurements of two-photon-induced luminescence, SHG and THG in ZnSe NWs are presented. In accordance with the theory, the angular dependencies of nonlinear phenomena were observed and influence of the environmental dielectric constant on the magnitude of the nonlinear signals was demonstrated. The relative amplitudes of the angular dependencies were also significantly influenced by NW bending and nonuniformity.