Diffraction effects in macroporous silicon with through pores

The macroporous silicon (ma-Si) is a type of a porous Si where vertical pores form a two-dimensional (2D) periodic structure on the surface, and the pore depth is on orders of magnitude larger than the inter-pore distance and pore diameter. The combination of a high-quality 2D periodic structure with a high refractive index contrast in ma-Si opens the way to its application as a 2D photonic crystal. A photonic band gap appears if light propagates in a direction perpendicular to pore axis. The spectral position and width of the gap are defined by the structure symmetry, inter-pore distance, and pore radius. For the light propagating parallel to the pore axis, ma-Si can be used as a shortpass filter, transparent in the short-wavelength range and blocking the long-wavelength radiation. In ma-Si filters, light propagates in air in pores surrounded by silicon, absorbing visible light. The pore dimensions, i.e., their diameter and length, define the filter transmission spectrum. As far as we know by now, only one study devoted to ma-Si transmission in the visible range exists. The present study is devoted to further experimental and theoretical investigation of the ma-Si transmission in the visible range for the light propagating parallel to pore axis.