Three-dimensional silicon photonic crystal operates at infrared wavelengths
Researchers at Sandia National Laboratories (Albuquerque, NM) and Ames Laboratory at the University of Iowa (Ames, IA) have fabricated a three-dimensional (3-D) infrared photonic crystal on a silicon wafer. The crystal has a layer-by-layer structure consisting of parallel rods etched in silicon dioxide, rotated by 90° in successive layers with every other layer shifted by half of the separation between the rods. The result is a structure that repeats every four layers. Shawn-Yu Lin and James G. Fleming of Sandia and their fellow scientists produced a crystal with a stop band from 10 to 14.5 µm, strong attenuation of light within this band--about 12 dB per unit cell--and a spectral response uniform to better than 1% over the 6-in. wafer.
Because of the large bandgap, such a crystal could be used as a bandpass filter integrated with a silicon waveguide or a photodetector. The attenuation constant allows the production of a high-quality resonant cavity, confining light to a fraction of a cubic wavelength. This could allow fabrication of single-mode light-emitting diodes. A 3-D photonic crystal could also modify or suppress the intrinsic thermal emission of a hot object, which might be useful in infrared emissivity engineering.