Evolution of etching kinetics and directional transition of nanowires formed on pyramidal microtextures

Two-scale roughened silicon (Si) textures are considered promising architectures for versatile applications because of their excellent self-cleaning, light-trapping, and biosensing capacities. In this study, we explore the directional control of nanowires formed on pyramidal microtextures through a single-step metal-assisted chemical etching (MACE). The measured current density of Si dissolution at catalytic etching enables quantitative monitoring of the etching kinetics of nanowire formation. The preferential orientation of fabricated nanowires on {111}-plane pyramidal textures was found to positively correlate with the molar ratio of [AgNO₃] to ([AgNO₃]+[HF]), referred to as ρ. A distinct transition from <100> to <111> axial directions at ρ≥0.2 and ρ=0.07, respectively, was revealed. The <111>-oriented nanowires on the pyramidal microtextures exhibited an excellent antireflection performance, with a reflectivity as low as 1.2 % at 600 nm. The results of this study may aid the design for the development of high-performance Si-based optoelectronic devices.