Macroporous silicon formation by electrochemical anodization of n-type silicon without illumination

This work reports the electrochemical anodization of low-doped n-type silicon in aqueous hydrofluoride (HF) solution without the use of external illumination to generate macroporous silicon with a thin mesoporous transition layer. We have shown that pore formation during the electrochemical anodization of low-doped n-Si in the dark is due to the avalanche breakdown mechanism. Studies of dissolution valence revealed a competition between divalent direct and tetravalent indirect dissolution processes. The effect of pore morphology on anodization parameters such as applied potential, HF concentration, and anodization time was systematically investigated. The fabricated porous silicon has well-separated and straight macropores of pore diameters ranging from 89 ± 9 to 285 ± 28 nm and with limited branching or interconnectivity. Pore diameter uniformity is maintained throughout the porous layer. XRD and Raman spectroscopy have shown that the porous Si fabricated here is highly crystalline, retaining its original crystallinity. The fabricated porous Si presented in this work with tunable pore sizes, depths, and surface features can have potential applications in various fields of microelectronics, photonics, and sensors.