Experimentally derived catalytic etching kinetics for defect-utilized dual-porous silicon formation

A kinetic model of defect-utilized dual-porous structure (DPS) formation of silicon, composed of amorphous porous structure (APS) and defect-followed mesoporous structure (DMPS), is proposed. It is found that a defect site is preferentially removed while creating the oblique DMPS of high aspect ratio, and the DMPS is wholly covered with the APS which is gradually grown through applied etching time but finally saturated. It is suggested that the APS growth is progressed by the chemically enhanced-oxygen diffusion, which is driven by catalytic chemical reactions, and the APS dissolution depends on the oxygen concentration of the APS itself. On the basis of these results, we describe the DPS formation using fundamental reaction kinetics and Fick's law of diffusion. Understanding the APS growth mechanism is profound and potentially useful for prediction and controlling of the porous Si growth in the conventional HF/HNO ₃/H ₂O etching system. The DMPS development at the defect sites is ca. 22 times faster than the defect-free sites due to varied physicochemical properties. This analytical approach is a new attempt to describe the porous silicon formation mechanism as well as the conventional HF/HNO ₃/H ₂O etching procedure and further opens a new domain for the viability of defect engineering.