Tunable porous silicon mirrors for optoelectronic applications

Tunable porous silicon mirrors were fabricated as building blocks for optical interconnects and as a first step towards efficient routing of information on a small size scale. The basic structures for the tunable mirrors are porous silicon microcavities infiltrated with liquid crystals. The optical properties of the mirrors are influenced by thermal or electric field modulation. When the device is heated or a voltage is applied, the orientation. of the liquid crystals changes, causing a change in the effective refractive index of the liquid crystals within the mirror. The position of the reflectance resonance of the porous silicon microcavity is particularly sensitive to such changes in the refractive index. A reversible 10nm shift of the reflectance resonance of the mirror, leading to a 30% change in the amplitude of reflectance, has been observed due to thermal effects. Not only do these results show potential for future devices, but they also confirm that the liquid crystals are able to rotate in the constricted geometry of the porous silicon microcavities. For voltage driven devices, careful attention needs to be given to the configuration of the electrical contacts. The effectiveness of various device geometries has been investigated. Using standard lithographic techniques, aluminum contacts with minimum feature sizes of 10 microns were patterned directly on the porous silicon surface. A study on the use of free-standing porous silicon films was also performed.