Phonon stop-band materials
A.A. Balandin1,O.L. Lazarenkova1,*, R. Boechat1
1Nano-Device Laboratory,Department of Electrical Engineering, University of California - Riverside,Riverside, California 92521 USA 54042
Using an analogy with photonband gap (PBG) materials, we introduce a concept of the phonon stop-band (PSB)materials for thermoelectric applications. The structure under consideration isa regimented quantum dot superlattice made out of Ge/Si or other relevantmaterial system. Based on our theoretical model developed for calculation ofthe acoustic phonon dispersion in quantum dot arrays  we demonstrate that itis possible to achieve gaps in the phonon density of states along certaindirections. We found the dependence of the PSB on the ratio of the elasticstiffness constants of the nanostructure constituent materials. Since the gapis only exhibited along the high-symmetry quasi-crystallographic directions itis a stop-band rather then a band gap. It is shown that for realistic quantumdot parameters (dot size is few nanometers) it is possible to achieve a stopband in the phonon energy range that affects the value of the thermalconductivity tensor. The latter opens up a novel way for thermal conductivityinhibition and thus, increasing the thermoelectric figure of merit.
. O.L. Lazarenkova and A.A.Balandin, Phys. Rev. B, 66, 245319 (2002).
The work in UCR was supportedin part by NSF NER projects ECS-0210282.
*Present address:Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA91109 USA