Evolution of Etching Kinetics and Directional Transition of Nanowires Formed on Pyramidal Microtextures

Abstract

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.

Fabrication of Orientation-Tunable Si Nanowires on Silicon Pyramids with Omnidirectional Light Absorption

“…The reflectance of Si pyramids with curved SiNWs (upper) and ⟨111⟩-oriented SiNWs (lower) are between that of with ⟨100⟩- and ⟨111⟩-oriented SiNWs. A similar trend was reported by other researchers that Si pyramids with ⟨111⟩-oriented SiNWs demonstrated lower reflection than that with ⟨100⟩-oriented SiNWs at normal incidence (θ = 0°) …”

“…When the temperature was increased to 25 °C or higher, all Ag films on Si pyramids would separate into nanoparticles, resulting in ⟨100⟩-oriented SiNWs (Figures d and f). Other researchers have also reported that Ag mesh preferentially moved along the direction normal to ⟨111⟩ planes, whereas isolated Ag nanoparticles sank along equivalent [100] directions of Si crystal , in a high concentration of H 2 O 2 at room temperature. If the catalyst metal did not dissolve, the etching behavior would be different.…”

“…A similar trend was reported by other researchers that Si pyramids with ⟨111⟩-oriented SiNWs demonstrated lower reflection than that with ⟨100⟩-oriented SiNWs at normal incidence (θ = 0°). 16…”

“…A 30% reduction in reflectance can be obtained by multiple reflection in the micrometer-sized pyramid structure in the whole solar spectrum, compared to polished Si wafer . Intensive efforts have also been devoted to the use of SiNWs due to their advantageous light trapping effect. , So far, a complex structure combining the advantages of pyramids and SiNWs has attracted significant research interest in achieving omnidirectional light absorption and overcoming the directional dependence of photovoltaic performance. − Methods to fabricate complex Si structures include dry-etching method and wet-chemical etching method. Dry-etching method, such as reactive ion etching, was widely used in industry and could make a variety of structures on Si wafer .…”

Deep Etching of Single- and Polycrystalline Silicon with High Speed, High Aspect Ratio, High Uniformity, and 3D Complexity by Electric Bias-Attenuated Metal-Assisted Chemical Etching (EMaCE)

“…Because the etching of Si by pure HF is extremely slow, selective etching of Si in a HF-h + system can be realized by controlling the distribution of h + concentration inside the Si substrate. Recently, a novel HF-based etching method, metal-assisted chemical etching (MaCE), has received extensive attention. − In MaCE, noble metal with defined shape and position is deposited on the top surface of Si. MaCE occurs when the metal-loaded Si is immersed in a HF–hydrogen peroxide (H 2 O 2 ) solution; h + is generated by reduction of hydrogen peroxide (H 2 O 2 ) under the catalysis of noble metals: …”