Effect of long- and short-range order on SiGe alloy thermal conductivity: Molecular dynamics simulation

We report the role of long- and short-range order on the thermal conductivity and mode relaxation times of a model Si0.5Ge0.5 alloy using molecular dynamics simulation. All interactions used the Stillinger-Weber potential and the Si and Ge atoms differed only by their mass. The simulated alloys were generated using a Monte Carlo approach to decouple the short-range order from the long-range order. The thermal conductivity is almost entirely determined by the alloy's nearest-neighbor short-range order. Changes to the mode relaxation times between similar to 3 and similar to 6 THz upon short-range ordering, and the observed f(-2) power law trend, suggest that short-range ordering reduces the anharmonic scattering rate of low frequency modes. The trend of thermal conductivity with short-range order may be transferred to real Si0.5Ge0.5 and other semiconductor alloys to the extent that scattering from mass disorder dominates their thermal conductivities.