We have obtained free-standing porous silicon filrns with porosity above 90% by us-ing allodic oxidizing, electropolishing, chemical etching and supercritical drying methods. Thesehighly porous films exhibited near 100% transmission in the near infrared and strong photoluminescence (PL). The porosity of these films increased with prolonging the time of chen1ical etching.Meanwllile, the blueshift of the optical transmission curves and the increasing of the PL intensitywas ohserved. However, there is no clear size dependence of the peak ellergy of the PL.
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