Stain Etching with Ferric Ion to Produce Thick Porous Silicon Films

Abstract

Stain etching of silicon in aqueous solutions composed of FeCl3 + HF + concentrated (HCl, HClO4 or H2SO4) leads to brilliantly luminescent porous Si with a unique dual layer structure. The upper layer (~2 µm or more thick) exhibits bluer luminescence (peaked at 520-590 nm). The lower layer exhibits redder luminescence (peaked at 630-660 nm). The peak PL wavelength and the PL intensity both depend strongly on the excitation wavelength. Photoluminescence excitation (PLE) spectroscopy indicates that the upper and lower layers are distinct because the PLE spectra of the two layers are different. Additionally, we demonstrate that two completely new stain etchants can produce visibly luminescent microporous silicon: V2O5 dissolved in HF(aq) and CeF4 dissolved in H2SO4(aq). In all cases bubble formation is suppressed and layer homogeneity greatly exceeds that obtained with nitrate based stain etchants.

Stain Etching of Silicon With and Without the Aid of Metal Catalysts

“…Stain etching will never rival anodic etching for ultimate control over the characteristics of porous silicon (por-Si) films. However, recent formulations of stain etchants developed by Kolasinski and co-workers (1)(2)(3)(4) have greatly expanded the possibility of using stain etching as a reproducible and cost effective process for the production of thin films and powders (5) of por-Si. The enhanced reproducibility and simplicity of metal ion containing oxidants as opposed to nitrates and nitrites has also facilitated a more quantitative approach to investigating and understanding stain etching.…”

(Invited) Rational Design of Etchants for Electroless Porous Silicon Formation

“…To help us answer this question we need to measure s R,0 for at least one other species. We have already demonstrated that Ce(IV) effectively produces por-Si (7,16). We have also found that HIO 3 etches Si in HF(aq) but that por-Si formation is hampered by precipitation.…”