  We present the design, fabrication and preliminary experiments of
two-dimensional photonic crystal cavities made in nanoporous silicon
luminescent at 700-800 nm. Enhancement in photoluminescence extraction
efficiency at the resonant wavelength is expected due to Purcell effect and
directed radiation pattern defined by the cavity. Such cavities should also
enhance nonlinearities exhibited by porous Si beyond what is observed in
one-dimensional distributed Bragg reflection cavities due to their small mode
volumes and modest quality factors. This design aligns itself well to
integration with conventional silicon based electronics on a single chip.
