We present both theoretical and experimental investigations of optical properties of excitons in semiconductor-insulator quantum wires. Spectra of linear and nonlinear absorption, photoluminescence and its polarization, photoluminescence excitation, time-resolved photoluminescence of GaAs, CdSe, and InP quantum wires 4-6 nm in diameter, crystallized in dielectric matrix, demonstrate the prominent excitonic behavior. In these structures an essential difference of dielectric constants of constituent materials leads to a considerable enhancement of excitons, the binding energies ranging from 120 meV to 260 meV and exciton transitions being well distinguished in nanowires with sufficient dispersion of diameter even at room temperature. A theoretical approach to calculations of the exciton parameters in a semiconductor-insulator cylindrical quantum wire of finite diameter is developed. This approach accounts for a band-gap renormalization due to the spatial confinement and self-image effect, as well as for a dielectric enhancement of the electron-hole interaction. The calculated exciton transition energies and absorption spectra are consistent with the experimental results.

The third-order optical nonlinearity χ(3) of porous silicon has been measured using the Z-scan technique. Intensity dependent absorption was observed and attributed to a resonant two photon absorption process. The real and imaginary parts of χ(3) have been measured at 665 nm and found to be 7.5×10−9 esu and −1.9×10−9 esu, respectively. This constitutes a significant enhancement over crystalline silicon. All optical switching based on nonlinear absorption is demonstrated.

No abstract

No abstract

No abstract