Macroporous Silicon: A Two-Dimensional Photonic Bandgap Material Suitable

We have fabricated macroporous silicon and proved its applicability as a two-dimensional photonic bandgap material in the near-infrared spectral range. Two different triangular lattices of circular air rods with lattice constants of 2.3 and 1.5 mm were etched at least 75 mm deep in an n-type silicon substrate by electrochemical pore formation in aqueous hydrofluoric acid. Photolithographic pre-patterning techniques and subsequent alkaline etching were used. In the case of the 1.5 mm lattice the photo-mask was modified so that series of etch pits were left out. These local perturbations of the initially regular lattice of air rods introduced photonic defects like waveguides. In the case of the 2.3 mm lattice we succeeded to micromechanically structure the macroporous layer to make 200 mm wide free-standing bars of porous material remain on the silicon substrate. These bars were used to measure the transmission of the photonic lattice dependent on the light polarization relative to the pore axes using FT infrared spectroscopy. The results excellently agree with theoretical cal-culations. The generation of KOH pits with lattice constants on a sub-mm length scale was demon-strated. 1