Quantitative analysis of gradient effective refractive index in silicon nanowires for broadband light trapping and anti-reflective properties

Abstract

Controlling the light reflection using vertically-aligned nanowires has great importance in fundamental research with interesting applications in photonic devices. Here, we discuss the spatial- and polarization-dependent reflectivity measurements from the cross-sectional as well as from the top surface of vertically-aligned disordered silicon nanowires. The gradient variation in an effective refractive index along the nanowire length is estimated using the cross-sectional reflectivity measurements. We have studied the gradient variation of an effective refractive index profile and its tunability with the nanowire length. The reflectivity is measured to be as low as 5% irrespective of spatial directions and the polarization of incident light in a broad wavelength range. This constitutes the signature of a broadband omnidirectional anti-reflector that is scalable with the nanowire length. The reflectivity measurements are in good agreement with theoretical calculations. Such omnidirectional anti-reflection in a broad wavelength range is useful for applications such as photon management in photovoltaic devices and disorder-induced light scattering.

Bactericidal Characteristics of Bioinspired Nontoxic and Chemically Stable Disordered Silicon Nanopyramids

“…The estimated values of R pk and R vk for SiNP surface were less than 1.5 μm, which is smaller than the size of the bacteria used in the study (Figure S1 and Table S1, Supporting Information). The spacing between two nanopyramids varies between 0.3 and 1.2 μm, similar to the variations observed in random nanostructures found on insect wings. ,, SiNWs were also fabricated and characterized using a reported procedure for comparative studies …”

“…4,26,32 SiNWs were also fabricated and characterized using a reported procedure for comparative studies. 41 The structural stability of SiNPs and SiNWs was also investigated under different chemical environment. The SiNPs and SiNWs were kept in a buffer (pH 7.4) and sulfuric acid (pH 2.75) solution for 20 days at 37 °C.…”

“…Finally, the substrates were thoroughly rinsed with DI water and immersed into DI H 2 O/HF (48%, 10:1, v/v) for 1 min in a Teflon vessel to remove native oxides. The disordered SiNWs were fabricated using a metal-assisted chemical etching technique as discussed elsewhere . The disordered SiNPs were fabricated using the wet etching technique that involved an alkaline aqueous solution of potassium hydroxide (KOH) as an etchant .…”

“…40 The disordered SiNWs were fabricated using a metal-assisted chemical etching technique as discussed elsewhere. 41 The disordered SiNPs were fabricated using the wet etching technique that involved an alkaline aqueous solution of potassium hydroxide (KOH) as an etchant. 42 The SiNPs were formed due to the difference in the etch rates of the ⟨100⟩ and ⟨111⟩ planes of Si.…”

Polymer-based self-assembled photonic crystals to tune light transport and emission

“…Photonic structures with different geometrical shapes, such as ellipsoidal cavities, nanowires, and cavities with micro-lenses, have been designed to enhance the collection efficiency. 128,[130][131][132][133][134] With growing research into single-photon emitters, a diverse range of solid-state emitters is now available, such as defect centers in diamonds, silicon carbide, and two-dimensional materials like hexagonal boron This journal is © The Royal Society of Chemistry 2022 nitride, which can be integrated with different types of photonic crystal structures. 88 These emitters can be integrated with low index-contrast self-assembled photonic structures to create efficacious monolithic devices with high-collection efficiencies and optimum control of the interaction of the single-photon emitting source with its surroundings to generate on-demand deterministic single-photon sources.…”