Photonic Crystals from Macroporous Silicon

Abstract

Regular, hexagonally-ordered macropore arrays have been obtained by photo-electrochemical etching of prepatterned silicon substrates. For typical pore diameters of about 1 μm, aspect ratios of about 100 have been achieved. Due to the high aspect ratio, the negligible surface roughness and the high dielectric constant of silicon, these macropore arrays are suitable candidates for photonic crystal devices. In this review, we present transmission spectra and the corresponding calculations of the bulk photonic crystals with a lattice constant of 1.5 μm having a complete photonic bandgap between a vacuum wavelength of 3 and 4 μm. By omitting some pores during the etching, photonic defect structures can be obtained, e.g., waveguides, beamsplitters or micro-resonators. As an example, a straight waveguide will be discussed and good agreement between theoretical calculations and experimental transmission spectra is shown. A confinement in the third dimension along the pore axis can be reached by modulating the pore diameter. This is achieved by applying a modulated current density during anodization and carefully taking into account diffusion processes in the pores. First transmission measurements along these modulated pores and the corresponding modeling are shown. The 3D photonic crystals have now in all three direction non-linear dispersion relations which can be tuned rather independently. For optoelectronic application, first macropore arrays with a lattice constant of 0.5 μm have been prepared, exhibiting a photonic bandgap around the interesting telecommunication wavelength region of 1.3μm.