Wide-band “black silicon” based on porous silicon

TLDR

Solar cells and optical detection devices often use antireflective surfaces to reduce reflection and enhance absorption. This letter reports a black silicon antireflective porous silicon structure fabricated by electrochemical etching. The structure is a gradient‑index multilayer whose refractive indices rise from the air side to the silicon substrate, and its reflectance depression is modeled with a transfer‑matrix simulation. Reflectance below 5 % is achieved across 3000–28000 cm⁻¹, and the simulated spectra agree well with measurements.

Abstract

Solar cells and optical detection devices often incorporate antireflective surfaces to reduce undesired reflection and enhance optical absorption. This letter reports a “black silicon” structure of antireflective porous silicon fabricated by using electrochemical etching. The sample has a gradient-index multilayer structure, i.e., the refraction indices of the structure increase from the top (near the air) to the bottom (near the Si substrate). Reflectance below 5% is obtained over a broad wave number range (3000–28000cm−1) and the depression mechanism of the optical reflectance is analyzed by simulating the structure with the transfer matrix method. The simulated result fits the measured spectra well.