Stain Etching with Fe(III), V(V), and Ce(IV) to Form Microporous Silicon

Abstract

Stain etchants made from ͑HF + V 2 O 5 ͒ or ͑HF + FeCl 3 •6H 2 O + HCl or H 2 SO 4 ͒ exhibited virtually no initiation time before the formation of porous silicon. Etching with Fe͑III͒ solutions for extended periods resulted in a unique dual layer structure that can reach a thickness Ͼ10 m and exhibited not only red-orange but also green photoluminescence ͑PL͒. Etching with ͑CeF 4 + H 2 SO 4 ͒ produced extremely uniform films. Visible PL was observed immediately after etching except for those films produced with ͑CeF 4 + H 2 SO 4 ͒, which required several days of air exposure before bright and robust PL developed.

Nanoporous silicon tubes: the role of geometry in nanostructure formation and application to light emitting diodes

“…We started etching the pillars in the BHNO solution to create highly homogeneous tube arrays. We then exposed the structures to the HVO solution to form a more uniform porous layer, see [24,44,67,67]. We used silicon pillars with the highest amount of doping, since according to Nahidi, the PL signal of the corresponding porous silicon is the strongest in this case [68].…”

“…Silicon dissolution in fluoride-containing electrolytes is primarily driven by the supply of holes in the silicon [42][43][44]. More details on the chemical reactions involved in stain etching can be found in the supplementary information (SI 2).…”

Porous Silicon Formation by Stain Etching

“…NH 4 HF 2 can be used to replace HF as long as the solution is acidified (Mills and Kolasinski 2004;Nahidi and Kolasinski 2006). An unusual example is that of CeF 4 dissolved in concentrated H 2 SO 4 (Kolasinski et al 2012;Dudley and Kolasinski 2009a). In this case, the oxidant and fluoride are supplied by the same species.…”

“…The former is used at a concentration of roughly 1 M, the latter closer to 0.1 M (Kolasinski et al 2010(Kolasinski et al , 2012Dudley and Kolasinski 2009a). Reproducible por-Si formation is possible with both oxidants when concentrated HF (aq) (49 wt% ¼ 29 mol L À1 in HF) is used as the acidic fluoride source.…”

“…Through experiments on a broad range of oxidants and a better understanding of the fundamentals of the charge transfer process, Kolasinski developed a set of guidelines for the formulation of effective stain etchants (Nahidi and Kolasinski 2006; Kolasinski et al 2010Kolasinski et al , 2012Dudley and Kolasinski 2009a;Kolasinski and Gogola 2012;Kolasinski 2005Kolasinski , 2010Kolasinski , 2014). …”