Formation Mechanism of Porous Silicon Layer by Anodization in  HF  Solution

Abstract

The mechanism of formation of porous silicon layer (PSL) has been studied according to the following experimental results. PSL is formed by the local dissolution of silicon which occurs only at the base of the pores. The HF concentration of the electrolyte in the pores of PSL is constant during anodization and the anodic reaction in the pores proceeds uniformly in the thickness direction. The dissolution of silicon in the pores is the results of the divalent and the tetravalent reactions of silicon with HF , without the disproportionation reaction. The insoluble surface porous film (SPF) exists at the surface of PSL and the silicic acid is formed in PSL. A model of forming PSL is proposed, with emphasis being placed on the anodic reaction and the local dissolution of silicon which is initiated by SPF and is promoted by the hindrance layers composed of the silicic acid.

Silicon Porosification: State of the Art

“…It was found that the pores at the surface usually have smaller diameter than those in the bulk of PSi (Figure 76h). 40,49,415,444 Such an increase in pore diameter from the surface to bulk is due to the transition from pore initiation to steady growth. The thickness of this transition layer is related to the size of pores; the smaller the pores are, the thinner is the surface transition layer.…”

Self-Assembled Hierarchical Nanostructures for High-Efficiency Porous Photonic Crystals

“…doped-Si, Al). [17][18][19] In this scheme, modulation of the anodic current through a substrate immersed in an acidic solution allows pores to be etched with size tunable from nm to µm. 19-21 materials, requires a complex and multi-step fabrication and generally yields layers with low refractive index (RI) contrast.…”

Microporous Silicon

“…Watanabe and Sakai were probably therefore the first to create highly microporous silicon, albeit without realizing it (Watanabe and Sakai 1971). Other workers who conducted early studies on the properties of layers anodized in p-wafers using highly concentrated HF included Unagami (1980) and Koshida et al (1985) who correctly referred to a "microporous structure" (Koshida et al 1986). The 1988 review of Bomchil et al (1988) clarified the trends in poresize distribution with anodization parameters for a range of mesoporous layers.…”