Third-order optical nonlinearity and all-optical switching in porous silicon

Abstract

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.

Optical and Dynamic Properties of Undoped and Doped Semiconductor Nanostructures

“…Similar nonlinear absorption have been observed for quantum wires of GaAs [105,106] and porous Si [107,108]. These non-linear optical properties have been considered potentially useful for optical limiting and switching applications [109].…”

“…For instance, the third order non-linear susceptibility, χ (3) (~5.6x10 -12 esu) for PbS nanoparticles has been determined using time-resolved optical Kerr effect spectroscopy and it was found to be dependent on surface modification [113]. Third order nonlinearity of porous silicon has been measured with the Z-scan technique and found to be significantly enhanced over crystalline silicon [109]. DFWM studies of thin films containing CdS nanoparticles found a large χ (3) value, ~10 -7 esu, around the excitonic resonance at room temperature [115].…”

Femtosecond photoluminescence spectroscopy of silicon nanocrystals

“…4. When direct absorption is negligible, we can determine the nonlinear absorption coefficient in case of a thin sample of thickness l by fitting the experimental data by the equation [10] ( ) ( )…”

“…Only few measurements with femtosecond time resolution of transient absorption in Si-NCs have been reported [5][6][7][8] and apparently no ultrafast PL dynamics have been measured. Two-photon absorption in Si-NCs was reported previously [9][10][11]. Here we concentrate on Si-NCs prepared by embedding porous silicon grains in a sol-gel derived SiO 2 matrix.…”

An All-Optical Silicon Nano-Transistor

“…The decrease of refractive index occurs because of carrier injection (forward bias) by diffusion from the highly doped regions into the intrinsic (low-doped) material. Th is is because the characteristic length for diffusive transport in the intrinsic region i = (DaTafi)^^^ = 5.2 iJ,m[Da = 18cm^/s is the ambipolar difPiision coefficient [9], and Tcff (= toN = 15.27 ns) is the effective carrier lifetime in the intrinsic region] is comparable to the lateral dimension of our device. On the other hand, the increase of refractive index results from depletion of carriers in the central guiding region.…”