Nanoscale strain and band structure engineering using epitaxial stressors on ultrathin silicon-on-insulator

Self-assembled, epitaxial nanocrystals can cause strain in the underlying substrate and locally alter its band structure. When the substrate is made very thin, these effects are considerably enhanced. We show that silicon-on-insulator (SOI), a composite of a thin, monocrystalline Si template supported by amorphous SiO2, approaches the ultimate limit of local strain accommodation––that of a free-standing, thin membrane––but has the mechanical robustness of a thick substrate. Ge nanocrystals grown coherently on SOI cause a significant local distortion, large band structure changes, and strong carrier confinement in the thin Si template. Nanoscale engineering of the electronic properties of thin Si is thus accomplished through the judicious growth of Ge nanocrystals on SOI.