Thermal conductivity reduction in Si-isotope-multilayers

Abstract

We employ the atomistic Greenʼs function (AGF) formalism to investigate phonon transport in silicon isotope multilayers. Since we use the AGF method, we can distinguish between coherent scattering at isotope multilayers and incoherent phonon–phonon scattering. Our investigations show that there are two different regimes for coherent scattering at isotope multilayers: the periodic regime, with periodically arranged layers, and a random regime, with layers of different thicknesses. The phonon scattering is stronger in the random regime, whereas in the periodic regime the phonon scattering rapidly saturates with the number of layers. Even though the phonon scattering in the random regime is stronger than in the periodic regime, the resulting thermal resistance in both regimes is much lower than the one obtained by combining the interfaces of the multilayer incoherently. We also found that the periodic regime is sensitive to small deviations. A small deviation from the perfect periodic arrangement leads to the behavior of the random regime. These deviations are so small that it is extremely difficult to actually grow perfect periodic isotope multilayers and observe the periodic regime experimentally.