Photoetching
of n-type silicon induces a photoluminescent (PL)
layer containing nanocrystals on the irradiated surface, usually through
band gap absorption (wavelength <1100 nm). Here, we demonstrate
the formation of a PL layer restricted to the backside surface, not
the irradiated surface, by using a 1064 nm Nd:YAG laser. A nanoscale
structure of the PL layer is achieved by merely modifying the electrolyte
concentration without adding oxidants. To illustrate the working principle,
we submit the hypothesis of a quasi-pn structure based on the theory
of a quasi-Fermi level. Because of the “injection current”
effect due to the quasi-pn structure, the hole current promoted by
free-carrier absorption flows toward the backside surface, leading
to anodization. This result is remarkable because anodization of n-type
silicon is very hard to achieve with just an etchant in the dark.