Growth of Ge quantum dot superlattices for thermoelectric applications

Cross-plane thermal conductivity reduction of vertically uncorrelated Ge∕Si quantum dot superlattices

“…However, in general it is slightly larger than previously published data for QDSLs. [6][7][8][9][10] The Ge content and the total surface coverage of the dots in our QDSLs ͑see Table I͒ are below those reported in earlier studies rendering difficult a direct comparison. If we extrapolate data from Lee et al 10 to 4%-5% coverage and 20 nm Si period, a value about 20 W / mK may be inferred.…”

“…The thermal conductivity is significantly reduced in superlattices 1-5 ͑SLs͒ and quantum dot SLs ͑QDSLs͒. [6][7][8][9][10] Previous studies by Lee et al on short period 3 -7 nm Si/ Ge SLs unveiled a decrease of Ќ with decreasing SL period. 1 A minimum value of about 3 W / mK was measured at 300 K. For larger periods, L Ͼ 13 nm, they unexpectedly observed a decrease of Ќ which was attributed to the existence of extended defects.…”

“…Further nanostructuring and phonon confinement may result in enhanced figures of merit and therefore Ge QDSLs have also been analyzed by a number of authors. [6][7][8][9][10] Liu et al 6,7 measured Ќ in Ge QDSLs with Ge content from 7% to 20% and a Si spacer of 20 nm. They reported values as low as 6.2 W / mK for samples grown at 500°C with an average composition of Si 0.93 Ge 0.07 and dot surface coverage about 10%.…”

Acoustic phonon scattering from particles embedded in an anisotropic medium: A molecular dynamics study

“…Quantum dot superlattices, which are regular arrays of semiconductor nanoparticles embedded in a semiconducting host material, are potentially the most promising materials for ZT enhancement. 6,13,14 These materials have recently demonstrated ZT values higher than 1, and this enhancement arises primarily from the reduction of k c . 6,15,16 The fundamental reasons for thermal conductivity reduction in quantum dot superlattices are still not fully understood, 17 but phonon scattering from the embedded particles, changes in the phonon dispersion relation due to nanostructuring, and quantum confinement are all likely mechanisms.…”

“…To investigate shapes similar to experimentally fabricated nanostructures, 14 models of pyramid-shaped scatterers were used. The resulting total phase functions shown in Fig. 14 correspond to cases with pyramids of height 3.5 and base dimensions 7 ϫ 7.…”