Macroporous silicon

The electrochemical formation of macropores in porous silicon is briefly reviewed. Various morphologies are obtained as a function of the substrate type and etching conditions. On n-Si, macropores are generally growing along preferential crystallographic directions. On p-Si, in aqueous conditions far from electropolishing, the growth direction is rather determined by the current lines in the space-charge region. A summary of macropore characteristics is given as a function of the preparation conditions. Various models have been developed in order to account for the morphologies and characteristic sizes. These joint experimental and theoretical works have provided a good understanding of macropore growth, opening the way to many applications, and the most significant ones are mentioned. An impressive level of control has eventually been achieved for the fabrication of regular macropore arrays of high aspect ratio, including the incorporation of intentional defects or porewall shaping.