Atomic structure of the interface between silicon (111) and amorphous germanium

The structure of the transition region between crystalline Si(111) and amorphous germanium has been studied by means of quantitative high-resolution electron microscopy. Using iterative image matching techniques the two-dimensional distribution function of germanium atoms in the transition region has been determined from focal image series of such interfaces. The distribution function reveals lateral ordering close to the crystalline substrate in addition to a pronounced layering usually observed for solid-liquid interfaces. It further shows that the transition region is elastically strained due to the volume misfit between crystalline silicon and amorphous germanium. The width of the transition region is 1.4 nm corresponding to about four (111) layers of crystalline silicon or germanium. Finally, the width of the bond-angle distribution for the first layer of germanium atoms on the silicon substrate is determined as 8.9degrees which is close to the corresponding value of 9.7degrees for bulk amorphous germanium.