Local-strain effects in Si∕SiGe∕Si islands on oxide

The tensile-strained Si, based on the misfit between Si and SiGe gives high speed and high drive current to the metal-oxide-silicon field effect transistors. In order to achieve the total system minimum energy, the island edge, within some characteristic length, bends upwards giving rise to a distorted lattice, as simulated by the finite element method. The finding indicates that the conventional strain partition rule of Si∕SiGe∕Si layers used for a large island size (>10μm) is not adequate for a small island size (<200nm) due to the significant local-strain effect of the edge lattice distortion. For a small island size, the bending from the edge can significantly affect the strain on the surface of the top Si layer, and a compressive strain or reduced tensile strain occurs at the center of the top Si layer, while the conventional strain partition rule predicts a uniform tensile strain on the top Si layer for any size of Si∕SiGe∕Si islands.