Effect of Silicon Conductivity and HF/HO Ratio on Morphology of Silicon Nanostructures Obtained via Metal-Assisted Chemical Etching

n-type silicon substrates were etched via metal-assisted chemical etching with silver as catalyst and aqueous solution of hydrofluoric acid (HF) and hydrogen peroxide (HO) as etchant. The effect of high (5 Ω cm) and low (0.005 Ω cm) substrate resistivity, [HF/(HF + HO)] ratio, and etching time on the etched-out features was investigated. For the high-resistivity silicon substrate, the etched-out features had nanowire morphology for [HF/(HF + HO)] ratios of 0.70–0.95. However, for the low-resistivity silicon substrate, features with nanowire morphology could be obtained only for [HF/(HF + HO)] ratios of 0.90–0.95. The observed morphological changes can be explained based on local etching initiated on the sidewalls of etched-out features by redeposited silver and excess holes.