Phonon Scattering in Bi2Te3/Sb2Te3 Superlattice

Ultrafast time-resolved measurements were conducted to investigate scattering mechanism of coherent optical and acoustic phonons in Bi2Te3, Sb2Te3 and Bi2Te3/Sb2Te3 superlattice (SL) films. Strong phonon scatterings in the Bi2Te3/Sb2Te3 SLs are attributed to the interfaces of their hetero-structures. Moreover, decreases of acoustic phonon velocity are observed in SLs, coming from phonon folding and softening. Our results show that both the enhanced interface scattering and the reduced phonon velocity contribute to suppressing the heat transport in SLs.

Experimental Study of Phonon-Folding in Si/Ge and Si/Sige Structures Designed for Thermoelectric Applications

We report data of Raman study of Si/Ge and Si/SiGe superlattices designed for thermoelectric applications. The obtained Raman spectra clearly indicate the presence of folded doublets from longitudinal acoustic phonons. Due to the significant difference in the sound velocities for Si and Ge the position of the doublets strongly depends on the superlattice layer thickness and ordering. Comparison of the Raman data for different samples with measured thermal and thermoelectric properties allows us to determine a correlation between the strength of the phonon confinement in these structures and their thermoelectric properties. Our experimental results are consistent with recent theoretical prediction of increased thermoelectric figure of merit in semiconductor quantum wells.

RAMAN SCATTERING ON PHONONS IN Nb-Cu METALLIC SUPERLATTICE

We present Raman scattering results on transverse acoustic phonons in metallic superlattice and have verified most expectations regarding acoustic phonon folding as in semiconductor superlattices. Raman folded peaks up to seventh order can be observed which agree closely with elastic continuum prediction in frequency. Owing to metal high optical absorption, phonon momentum nonconserving have caused increasing linewidth and disorder-activated transverse-acoustic mode scattering.