Strained hetero interfaces in Si/SiGe/SiGe/SiGe multi-layers studied by scanning moiré fringe imaging

Nanometer-scale scanning moire fringes (SMFs) of the hetero interfaces in Si/Si1−xGex/Si1−xGex/Si1−xGex multi-layers have been obtained by high-angle annular dark field scanning transmission electron microscope. The SMFs that appeared at each interface were commensurate, when the layers had no defects from epitaxial growth. The SMF images showed that the Si substrate at the interface was tensilely strained, and it was measured to be 0.2% relative to the unstrained Si substrate. In addition, it was found that the (220) lattice plane of the Si1−xGex layers was linearly increased with a gradient of 0.015%/nm in grown direction of [001].