Trends in fabrication and applications of macroporous silicon

Two promising applications of porous silicon exploiting the optical and fluidic properties of macropore arrays which penetrate the full wafer thickness are introduced. The first application aims at optical filters, based on diffraction at small apertures. The filters consist of straight pores with diameters in the micrometer regime and a length of up to one millimeter through a silicon wafer. In contrast to Bragg-, Woods-, or glass-filters, the light is not transmitted in matter but in the medium inside the pores. The filters therefore show a true shortpass characteristic. In the second application the large inner surface of the porous matrix acts as immobilisation and reaction site for specific biological molecules. The optical and fluidic properties of through-pores in well ordered arrays are found to be advantageous for rapid reaction and sensitive detection.