High efficiency chemical etchant for the formation of luminescent porous silicon

Hydrofluoric acid solutions containing high concentrations of the ion NO⁺ produce an etchant capable of reproducibly generating a porous silicon layer on both single-crystal and polycrystalline silicon surfaces. Room-temperature photoluminescence from porous silicon that has been chemically etched in such solutions has been observed. The photoluminescent intensity is superior to that obtained using HNO₃/HF based stain etches. Reproducibility with respect to etch induction time, and the quality of the porous silicon layer are also improved when compared to classic stain etchants. Although, prior work has suggested that HNO₂ is the active oxidant in silicon stain etching processes, the present work points to NO⁺ as the active species.