Enhanced Nonlinear-Optical Interactions in Nanostructured Semiconductors
V. Yu. Timoshenko, L. A. Golovan, S. V. Zabotnov, V. A. Melnikov, A. Zheltikov,
and P. K. Kashkarov
Moscow State M.V. Lomonosov University, Faculty of Physics, 119992 Moscow, Russia
Phone/Fax: +7(095)9391566, E-mail: vtim@vega.phys.msu.su
Novel artificial photonic and nonlinear optical media can be formed by
nanostructuring bulk semiconductors. We report on linear and non-linear optical
properties of electrochemically prepared porous Si (PSi) and porous GaP. These
materials are composed from nanocrystals and nanopores whose dimensions can be
tuned from several nanometers to several micrometers by using different preparation
conditions, e.g. substrate doping level, etching duration and current density. PSi layers
formed from low symmetry c-Si wafers are found to exhibit optical properties of
uniaxial birefringent crystals operating in visible and infrared spectral range. Both the
birefringence and dichroism are explained by the form anisotropy of Si nanocrystals
assembling PSi layers. The optical axis direction and birefringence value depend on
the crystallographic orientation of Si substrate and PSi preparation conditions. The inplane birefringence of (110) PSi layers can be strong enough to compensate for the
normal dispersion of material in the visible and middle IR ranges. This remarkable
fact allows phase-matched nonlinear optical wave interactions in the birefringent PSi
to be achieved. Additionally, an increase of the nonlinear optical susceptibility and
modifications of its anisotropy parameter are possible for the birefringent PSi because
of the local electric fields in ensembles of anisotropically shaped Si nanocrystals. An
enhancement of the effective nonlinear optical susceptibilities is possible in
macroporous GaP because of the light localization phenomenon.