Diffusion of Ge below the Si(100) surface: Theory and experiment

We have studied diffusion of Ge into subsurface layers of Si(100). Auger el ectron diffraction measurements show Ge in the fourth layer after submonola yer growth at temperatures as low as 500 degrees C. Density functional theo ry predictions of equilibrium Ge subsurface distributions are consistent wi th the measurements. We identify a surprisingly low energy pathway resultin g from low interstitial formation energy in the third and fourth layers. Do ping significantly affects the formation energy suggesting that n-type dopi ng may lead to sharper Si/Ge interfaces.