Composite Porous Structure Formation by Platinum-Particle-Assisted Etching of a Highly-Doped p-Type Silicon: Evaluation of Charge Flow in Silicon

Abstract

Electroless deposition of metal particles on silicon (Si) followed by the metal-assisted etching (metal-assisted chemical etching) is a simple way to fabricate Si nanostructures. A composite porous structure consisting of straight macropores and a mesoporous layer can be created by platinum (Pt)-particle-assisted etching. In this work, we studied the composite structure formation on a highly-doped p-Si (ca. 5×1018 cm−3) in comparison with a moderately-doped p-Si (ca. 1×1015 cm−3). The composite structure drastically changed: the ratio of mesoporous layer thickness to macropore depth increased to 1.1 from 0.16 by using the highly-doped Si instead of the moderately-doped Si. The open-circuit potential of Si in the etching solution shifted to the positive direction by the Pt deposition. The potential shift of highly-doped Si was smaller than that of moderately-doped Si, which can be explained by the polarization characteristics. We calculated the band bending in Si by using a device simulator that reproduced the conditions of Pt-particle-assisted etching. The results indicated that, in the case of highly-doped Si, the consumption rate of positive holes at the Si surface away from the Pt particles increases due to the tunneling effect, which is consistent with the thick mesoporous layer formation.

Metal-Assisted Etching of n-Type and p-Type Silicon Using Patterned Platinum Films: Spatial Distribution of Mesoporous Layer and Open Circuit Potential of Silicon

“…Previously, we studied the metal-assisted etching using Pt particles as the catalysts and measured the potential of Si during etching. 21,22,48 For example, the potentials of Pt-particle-deposited n-Si and p-Si were −0.25 V 48 and 0.07 V 21 vs Ag/AgCl, respectively. The potentials of Pt-filmdeposited n-Si (after the potential drop) and p-Si are similar to that of Pt-particle-deposited n-Si and p-Si, respectively.…”

“…In platinum (Pt)-particle-assisted etching, a composite porous structure consisting of macropores and a mesoporous layer can be created. 11,[15][16][17][18][19][20][21][22] The macropores are formed by the dissolution of Si under the Pt particles, while the mesoporous layer is formed on the Si surface away from them. Recently, we demonstrated that the ratio of macropore depth and mesoporous layer thickness changes depending on the composition of etching solution 21 and doping density of Si.…”

“…Recently, we demonstrated that the ratio of macropore depth and mesoporous layer thickness changes depending on the composition of etching solution 21 and doping density of Si. 22 Effects of the doping type of Si on the metal-assisted etching behaver has also been studied through various approaches. [23][24][25][26][27][28][29][30] However, the difference of composite porous structures formed on n-Si and p-Si has not been discussed enough.…”

“…In the composite porous structure formation by the Pt-assisted etching, Pt particles deposited through displacement reaction 31 have been mainly used. 11,[15][16][17][18][19][20][21][22] For the present investigation, we reconsider the geometry of Pt catalysts. As mentioned above, positive holes have an important role in the dissolution of Si.…”

Platinum-Particle-Assisted Etching of Low-, Moderately-, and Highly-Doped p-Type Silicon: Change of Composite Porous Structure

“…[1][2][3][4]7,8,10,[22][23][24][25][26][27][28][29][30][31][32] For example, when using platinum (Pt) catalysts, not only straight pores formed by the preferential dissolution of Si beneath the Pt catalysts but also mesopores covering on the entire surface of Si can be obtained. [33][34][35][36][37][38][39][40] However, the formation mechanism of the composite porous structure is not fully understood. We previously demonstrated that a characteristic composite structure (mesoporous layer thickness exceeds straight pore depth) is formed on highly-doped p-Si and the thick mesoporous layer can be attributed to the tunneling effect at the Si/electrolyte interface.…”