Photonic Energy Density and Scattering from Random and Periodic Arrays of Silicon Pillars

Control of the photonic energy density is relevant for applications in lighting, sensing, and energy harvesting. Since the energy density is proportional to the local density of states (LDOS), it is natural to explore 2D photonic materials as a potential large-scale platform. Therefore, we study materials consisting of silicon pillars with a height of more than $50\ \mu \mathrm{m}$ and diameters varying from $2\ \mu \mathrm{m}$ to $6\ \mu \mathrm{m}$ that are made with CMOS-compatible reactive ion etching. The pillars are arranged in large random (Fig. 1a) and periodic arrays (Fig. 1b) consisting of up to 430.000 pillars and with a wide range of packing fractions. Depending on the long-range order, the pillars show a dramatic difference in appearance and in photonic interaction: using a white light incident from the top, periodic arrays appear iridescent and random arrays matt grey (Fig. 1c). When illuminated in the 2D plane with monochromatic laser light, the lateral scattering observed out of the plane is proportional to the photonic energy density in the pillar arrays [1]. Our samples have good potential to critically test theories of the photonic energy density in complex media [2], and ultimately even anisotropic Anderson localization of light [3].