Rapid prototyping of highly ordered subwavelength silicon nanostructures with enhanced light trapping

Abstract

High index nanostructures lead to unique light-matter interactions and strong optical resonances for potential light trapping applications and improved optical performances. In this work, Gaussian shaped subwavelength 3D nanostructures are introduced and rapid prototyping of these nanostructures is carried out on silicon (Si) in a single-step using focused ion beam (FIB) milling. The tapered geometry of Gaussian pillar structures provided reflection suppression from the smaller tip in contrast to its extended base, enabling trapping of light, confirmed through light reflection calculations and hot spots observed through absorption density distributions. The nature of accelerated ions in a FIB system is directly used and highly ordered Gaussian pillar like subwavelength nanostructures are fabricated in a single-step on Si. Simulations and experiments demonstrate nanostructure evolution from periodically spaced subwavelength nanoholes to Gaussian pillar structures with tuning of beam processing parameters, providing fabrication flexibility. The proposed light management structures, investigated through Finite Difference Time Domain (FDTD) calculations, exhibit 10–20% reflection for a broadband visible wavelength range against planar Si and previously reported Si structures (such as nano-cones, nano-wires, nano-pyramids etc.). Experimental results support theoretical predictions and provide evidence for antireflection properties from the fabricated nanostructures. Considering the rapid fabrication approach and tunable nature of Gaussian shaped nanostructures, exhibiting unique optical properties; this work provides realization of nanoscale light management 3D structures for localized light trapping and antireflection applications.