Fabrication and Characterization of Mid-Infrared Stealthy Hyperuniform Surface Patterns for Enhanced Light Absorption in Semiconductor Solar Applications

Abstract

Silicon solar cells lose approximately 30% of incident sunlight to front-surface reflection before any absorption can occur. Stealthy hyperuniform (SHU) surface patterns – engineered disordered structures that suppress long-range density fluctuations – have been proposed as a broadband, angularly robust solution to this problem, combining the spectral uniformity of disordered systems with the design control of photonic crystals. This thesis presents the fabrication, characterization, and analytical modeling of SHU-patterned semiconductor surfaces for mid-infrared and solar applications. Angle-resolved Fourier-transform infrared (FTIR) spectroscopy measurements on SHU-patterned InP substrates demonstrate that the patterned surface preserves its spectral transmission shape from 0° to 45° incidence – consistent with the isotropic scattering behavior predicted by SHU theory – while exhibiting Fresnel-consistent polarization dependence in both TE and TM transmission and a clear Brewster angle minimum in reflectance near 50°-55° mirror angle. A transfer matrix thin-film model is developed for SHU pillar arrays on silicon using the effective medium approximation Neff = f · nSi + (1−f) · nair, where f is the pillar fill factor. The model identifies a fundamental tradeoff between spectral ripple and average transmission, with the antireflection condition at f ≈ 0.35 maximizing broadband light admission into the silicon substrate. The model is then extended to solar wavelengths (300-880 nm) by incorporating the complex refractive index of silicon from Aspnes and Studna (1983), enabling direct computation of absorption A = 1−R−T as a function of fill factor and pillar height. Solar-weighted absorption, integrated against the AM1.5 standard solar spectrum, increases from 54.7% for bare silicon to 85.5% at the antireflection condition (f ≈ 0.35, d = 100 nm), and reaches a maximum of 93.7% at the optimal geometry (f ≈ 0.19, d ≈ 96 nm) – a gain of 39 percentage points over an uncoated surface. These results establish a validated measurement framework and concrete fabrication targets for the next phase of the project, in which SHU-patterned silicon surfaces will be characterized at solar wavelengths.