Tunable reflection minima of nanostructured antireflective surfaces

Abstract

Broadband antireflection schemes for silicon surfaces based on the moth-eye principle and comprising arrays of subwavelength-scale pillars are applicable to solar cells, photodetectors, and stealth technologies and can exhibit very low reflectances. We show that rigorous coupled wave analysis can be used to accurately model the intricate reflectance behavior of these surfaces and so can be used to explore the effects of variations in pillar height, period, and shape. Low reflectance regions are identified, the extent of which are determined by the shape of the pillars. The wavelengths over which these low reflectance regions operate can be shifted by altering the period of the array. Thus the subtle features of the reflectance spectrum of a moth-eye array can be tailored for optimum performance for the input spectrum of a specific application.

Suppression of reflection peaks caused by moth-eye-type nanostructures for antireflection applications studied by using FDTD simulation

“…The reflectance shows an oscillating behavior in the visible region, and the average reflectance decreases as the pitch increases from 200 to 350 nm. Similar successive maxima and minima in the reflectance spectrum are frequently observed from the moth-eye anti-reflection coatings [8][9][10][11]. The dependence of the reflectance maxima on the pitch is related to the interference by the two interfaces of the moth-eye layer [9].…”

“…In many moth-eye nanostructure cases, successive local maxima and minima are observed from the reflectance spectrum [8][9][10][11]. Their appearance is attributed to the thin-film interference and is known to be sensitive to the pitch of the array [9].…”

“…Their appearance is attributed to the thin-film interference and is known to be sensitive to the pitch of the array [9]. The oscillating reflectance may be troublesome because it will cause coloration of the reflected light toward specific viewing directions.…”

Engineered biomimicry for harvesting solar energy: a bird's eye view

“…Similar low-reflection surfaces textured with arrays of nanopillars with different periods (pillar-to-pillar distance, from 150 nm to 350 nm), heights (from around 150 nm to 500 nm) and shapes (pillar width-to-period ratio from around 0.3 to 0.7) were fabricated by electron-beam lithography on silicon wafers [34]. In parallel, numerical simulations using the rigorous coupled-wave analysis (RCWA) indicated that as the height and shape of nanopillars as well as the array period affect reflectance, these parameters require optimization for best performance in the specific wavelength range over which the surface is required to function.…”

Omnidirectional antireflective properties of porous tungsten oxide films with in-depth variation of void fraction and stoichiometry

“…Thin films exhibiting thickness-graded refractive index profiles are being intensively studied recently, for applications in antireflective coatings with enhanced omnidirectionality and broadband characteristics [4]. The refractive index profile and hence the reflection suppression, is controlled either by depositing layers of different materials or by controlling the in-depth void fraction variation using multiple deposition steps, by employing various types of lithography and subsequent pattern transfer such as plasma etching, by incorporating particles and properly tuned deposition processes etc [5][6][7][8][9][10][11]. Even though most of these coatings exhibit good AR performance, the scale-up and the integration of most of these processes are either difficult or subject to serious economic constraints.…”