Forming a Photoluminescent Layer on Another Surface in the Dark through Lasering of N-Type Silicon in an Electrolyte

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.