A method was presented for fabricating uniaxially, as well as biaxially, strained Si films on porous Si substrates. Single crystalline Si films of ~50nm thickness, on top of porous Si substrates, could be routinely obtained by self-limiting anodization of heavily doped p-type substrates with epitaxially grown thin Si overlayers. The typical structure of the samples had the porous Si region in a square shape in the center of the sample surrounded by bulk Si; analogous to a picture in a frame. The porous Si region underwent volume expansion upon oxidation at low temperatures (~500C) in steam. The rigid bulk Si frame constrained the porous Si region; preventing it from expanding along the direction of the substrate surface. The expansion could be uniaxial or biaxial along the sample surface if 2 opposite stripes of bulk Si or all 4 sides were removed. A uniaxial tensile strain of 0.83%, observed in a 150nm-thick Si film without dislocations or cracks, was described.

Fabrication of Dislocation-Free Si Films under Uniaxial Tension on Porous Si Compliant Substrates. J.Kim, J.Y.Lee, Y.H.Xie: Thin Solid Films, 2008, 516[21], 7599-603