High efficiency chemical etchant for the formation of luminescent porous silicon

Abstract

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.

X-ray investigation of nanostructured stain-etched porous silicon

“…8 The Si wafers were etched in a disk of 11 mm in diameter. Since the etching is very sensitive to the type and doping concentration of the silicon wafer, 20 a small amount of NaNO 2 ͑0.1 g / l͒ was added to the etch solution in order to homogenize the stain etching, according to the procedure described by Kelly et al 7 A series of PS samples with etching times ranging from 1 to 10 min was produced. The porous Si layers were 1 -4 m thick as evaluated from scanning electron microscopy.…”

“…By stain etching, a solution containing HF, HNO 3 , and water is used in a process where an oxidation of silicon atoms occurs by hole injection from nitric acid and, simultaneously, its reduction produces NO and water. The stain etching can be an advantageous method in the formation of porous silicon layers, [6][7][8] mainly for substrates with higher doping level.…”

Properties of light-emitting porous silicon photoetched in aqueous HF∕FeCl3 solution

“…3͑a͒ and 3͑c͔͒ exhibit a broad emission peaking at ϳ2.0− 2.1 eV, which is typically observed in stain etched PSi samples in HF/ HNO 3 -based solutions. 3,[9][10][11][12][13][14] The stain etched sample in the 47 wt % solution ͓Fig. 3͑d͔͒ also exhibits a broad peak at ϳ2 eV.…”

Porous silicon in drug delivery devices and materials☆

“…In the stain etching procedure, a chemical oxidant (typically nitric acid) replaces the power supply used in the electrochemically driven reaction. HF is a key ingredient, and various other additives are used to control the reaction [49]. Stain etching generally is less reproducible than the electrochemical process, although recent advances have improved the reliability of the process substantially [50].…”