Two-photon-excited photoluminescence from porous silicon

Two-photon-excited photoluminescence can be readily observed from porous silicon (PSi) with pulsed lasers. While its spectrum and lifetime are identical to those under one-photon excitation,;it has a degree of polarization significantly higher than the latter and depending on the orientation of the input polarization with respect to the crystalline axes of the sample. The degree of polarization is a maximum when the input polarization is along [110] in the surface plane of PSi prepared from a Si (100) wafer and a minimum along [010]. The results can be understood from selective excitation of ellipsoidal nanoparticles by linearly polarized light and intrinsic anisotropy in two-photon excitation of crystalline Si. [S0163-1829(98)05844-5].