Fabrication of octagonal and dodecagonal single crystal Si micropyramids via etching without using a pre-patterned mask

Surface texturing of Si has attracted significant attention over the past decades as micro/nano patterns allow for preferred opto-electronic and electrochemical properties. Here a new fabrication method, based on etching in aqueous NaOH-polyethylene glycol solution is presented, which allows the formation of novel eight and twelve sided Si micropyramids. Particularly, the presence of NaOH resulted in the formation of four sided facets along intersecting {111} planes, while with continuous etching the high molar mass polyethylene glycol resulted in the formation of four additional facets identified to be (212) planes producing octagonal pyramids. Further etching of these octagonal pyramids lead to the formation of twelve-sided pyramids. Eight-faceted (octagonal) pyramids have been reported in the literature, but only through the use of photolithography, while twelve-faceted (dodecagonal) pyramids have not been observed for any type of crystal.