Molecular dynamics simulation is used to study the scattering of phonon wave packets of well–defined frequency . The simulation system is 22 unit cells in the direction normal to phonon propagation and 3000 unit cells (1.63m) in phonon propagation direction. For simplicity, the defects differ from the Si only in their mass, which is taken to be four-times that of Si. The mass defects are randomly distributed in the middle region of simulation system along z direction. The phonon wave packet propagating and scattering in the defect region are explicitly determined. Fig .1 shows a snapshot of displacements for a LA wave packet with a frequency of 4.4THz transmitting through the point defect region (located in -100< z < 100) . We calculate the relative amounts of energies in the transmitted and reflected waves, determine the main parameters which influence the phonon scattering process, and analyze their effect on thermal transport. The results show that transmitted and reflected energies strongly depend on the frequency of phonon and concentration of mass defects. These results are compared with the classic relationship for the scattering strength for point defects derived by Klemens in 1950s. This work sheds light on the effects of point defects on thermal conductivity of semiconductors.
Journal: TechConnect Briefs
Volume: 1, Technical Proceedings of the 2006 NSTI Nanotechnology Conference and Trade Show, Volume 1
Published: May 7, 2006
Pages: 677 - 680
Industry sector: Advanced Materials & Manufacturing
Topic: Informatics, Modeling & Simulation