High-aspect-ratio silicon microwire arrays by metal-assisted chemical etching for photovoltaic applications

Abstract

Vertically aligned silicon microwire (MW) arrays have been extensively investigated as a means for developing highly efficient and low cost solar cells. Silicon surface patterned with the MW arrays leads to broadband antireflection as well as enhanced light trapping efficiency. Vertically-aligned MWs can be fabricated by several methods, such as vapor-liquid-solid (VLS), reactive ion etching (RIE), and metal-assisted chemical etching (MACE). Among them, owing to the low cost and wafer-scale fabrication, MACE is an attractive method to fabricate Si MWs. However, the detailed mechanism of Si MW etching using a metal thin film as a catalyst is still unclear. Here, we present a systematic study of MACE to fabricate Si MWs. Several models on efficient redox reactions of reactants with silicon though the metal catalyst were studied by controlling MACE parameters, such as the thickness and morphology of metal thin film and electrolyte concentration (HF and H2O2). As a result, by optimizing MACE conditions, we successfully fabricated high-quality Si MWs with lengths up to 17 μm. The minority carrier lifetime of these MWs, measured by the microwave photoconductive decay, is higher than that of MWs etched by DRIE process. The MACE method of high-quality Si MWs would offer opportunities to develop cost-effective, highly efficient solar cells.