Nanometer-Thick Nickel Coatings on Silicon Micropyramids for Infrared Absorption

Although silicon micropyramids and related microstructures are well known for antireflective properties, the effects of texture and coatings remain unclear in the infrared range. Here, we investigate the optical properties of silicon micropyramids and show that their infrared absorptivity increases from 0.21 to 0.46 with a 20 nm nickel coating due to partial electromagnetic penetration but decreases to 0.07 with a 100 nm nickel coating. We also show further absorption tunability with additional texture at the nanoscale. These findings indicate that nanometer-thick metal coatings on textured silicon offer unique properties that are not attainable by either material individually and are important for optical and thermal management.