ORDER ALLOY IN Ge_xSi_1-x/Si(100) STRAINED-LAYER SUPERLATFICES

The Ge_xSi_1-x/Si(100) strained-layer superlattices have been investigated by means of the transmission electron microscopy of the cross-sectional specimen (XTEM) and the high resolution electron microscopy (HREM), The order alloy with a period of modulation twice as large as the lattice constant alongzone axis has been found in the alloy layers of the superlattices with x≈0.4-0.5. This order struc-ture makes the superlattices inhomogeneously strained. The result of the compuler simulation shows that the order alloy exhibits an altemating stack of 2 monolayers of Ge atoms and 2 monolayers of Si atoms along thezone axis. Thc calculated elastic strain energy of the disorder alloy reported in the litera-ture is very close to that of the order alloy alongzone axis. Thus, during the MBE growth of the alloy layers, both the disorder and order alloys can be formed alongzone axis.