Fabrication of lotus-type porous silicon by unidirectional solidification in hydrogen

Lotus-type porous silicon with many directional cylindrical gas pores was fabricated by unidirectional solidification of the melt dissolving hydrogen in a pressurized hydrogen atmosphere. The pores are elongated to the solidification direction and the size of the pores ranges from 10 μm to 1 mm in diameter, which is much larger than that in conventional nano-sized porous silicon. The porosity of 34% decreases to 10% with increasing pressure of hydrogen from 0.1 to 1.0 MPa. The average pore diameter also decreases with increase of the pressure. It is concluded that the pore evolution is attributed by the precipitation of the super-saturated hydrogen in the solidified silicon through melt.