Nano-sized pore formation in p-type silicon for automotive applications

Self-organized electrochemical etching of p-type silicon (Si) has been used to study random micro-pore formation which produces porous Si structures with nanometer well thickness. The density of micro-pores, i.e. the porosity can be varied in a wide range by choice of the substrate doping level. Surface enlargement up to a factor of 10000 and more can be easily achieved by choice of appropriate conditions in the anodic etch process. In addition we demonstrate deep anodic etching (DAE) of a pinhole array in Si by lithographic pre-patterning and subsequent etch using potassium hydroxide (KOH). The Si wafer is then anodically etched which produces deep channels, thus creating porous structures with enlarged surface. Such channels have large application potential as a carrier structure for the catalyst in micro-steam fuel reformers in compact fuel cells used as auxiliary power units for the on-board electronics in vehicles or can be used for fuel injection or fuel heating systems.