STRUCTURE OF SI1-XGEX ALLOYS

We generate liquid Si1-xGex alloys by simulated quench from the melt using ab initio molecular dynamics. In the case of crystalline SiGe alloy, we confirm that the rhombohedral structure is stabler than the zincblende structure with the same lattice constant. This result is in good agreement with other theoretical calculations. We observe the phase separation at liquid temperature (1500 K) when Ge composition is greater than 15%. The clustering effects are also strongly composition-dependent. These phenomena are clearly seen in the radial distribution function and the bond angle distribution. We explain the peculiarity with use of the P-Sn structure and the cluster model. The coordination number also shows the phase separation initiated at x>0.15.