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

Abstract

Metal-assisted etching (metal-assisted chemical etching) is an efficient method to fabricate porous silicon (Si). When using platinum (Pt) particles as metal catalysts in metal-assisted etching, a composite porous structure of straight macropores formed beneath the Pt particles and a mesoporous layer formed on the entire surface of Si can be fabricated. The formation mechanism of the composite structure is still open to discussion. We previously demonstrated that the ratio of mesoporous layer thickness to macropore depth showed a large value (approximately 1.1) in the case of highly-doped p-Si. In this study, we investigated the composite structure formation by using p-Si substrates with different doping densities and etching solutions with different concentrations of hydrogen peroxide (H2O2). There was not significant difference in the structures formed on low- and moderately-doped Si, despite the large difference in doping density. The ratio of mesoporous layer thickness to macropore depth increased within the range approximately from 0.1 to 0.4 with increasing the H2O2 concentration in the case of low- and moderately-doped Si, but it did not change in the case of highly-doped Si. We discussed the observation results based on the spatial distribution of hole consumption and the band structures at Pt/Si and Si/electrolyte interfaces.