Abstract

The electrochemical process used to form porous Si layers (PSL) is known for more than 30 years. The spongelike microscopic structure of PSL depends on the substrate properties, the doping concentration and the type of doping, as well as on the etching parameters. The pore size can range from μm to nm depending on the substrate parameters. For a given doping concentration the porosity can be varied by changing the current density. E.g., for p = 10¹⁹cm^-3 the porosity can be varied from about 30 to 80% by changing the current density from 10 to 250 mA/cm². The remaining Si structure is still single crystalline. Therefore, PSL have been used as patterned substrates for the heteroepitaxial growth of III-V layers on Si wafers. In addition, PSL can be used for the formation of silicon-on-insulator (SOI) structures.

© 1995 Optical Society of America