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

Abstract

A drastic reduction in temperature dependent cross-plane thermal conductivity κ⊥ occurs in Ge quantum dot superlattices (QDSLs), depending on the vertical correlation between dots. Measurements show at least a twofold decrease of κ⊥ in uncorrelated dot structures as compared to structures with the same Si spacer of 20nm but good vertical dot alignment. The observed impact of disorder on the conductivity provides an alternative route to reduce the thermal conductivity of QDSLs. The results of this work have implications for the development of highly efficient thermoelectric materials and on-chip nanocooling devices.

Tailoring thermal conductivity by engineering compositional gradients in Si1−x Ge x superlattices

“…The temperature dependence of the thermal conductivity κ displayed in Fig. 3(a) for samples with 26-and 45-nm periods is comparable to that observed in other planar SLs and quantum-dot SLs (QDSLs) [16]. The conductivity values measured at 300 K for the three samples considered in this work are shown in Fig.…”

“…2015, 8(9): 2833-2841 increases this value to 0.95 [7]. Additionally, the incorporation of a high interface density in epitaxial heterostructures has been recognized as an efficient approach to enhance boundary phonon scattering at low frequencies with a corresponding decrease in thermal conductivity [8][9][10][11][12][13][14][15][16][17]. SiGe planar superlattices (SLs) have thus emerged as potential candidates for both TE cooling of microelectronic devices and medium-temperature TE power generation [18,19].…”

Combined Kinetic Monte Carlo—Molecular Dynamics Approach for Modeling Phonon Transport in Quantum Dot Superlattices

“…The well-documented quantum dot superlattice publications of Khiuin, Liu, and Wang (primarily found in Refs, [77] and [78]) do provide this information and were thus chosen for comparison. Although it presents fewer images and less geometric information, the related work of Alvarez-Quintana et al, [79] may also serve as a useful reference for future MC models, íQiitun, Liu, and Wang used molecular beam epitaxy to grow stacks of alternating sheets of Si and a 50%-50% Si-Ge mixture. Upon deposition, the Si-Ge mixture formed isolated islands on the Si surface with a flattened plate-like dot shape on the order of 100-200 nm wide and lOnm thick.…”

Constitutive equations for heat conduction in nanosystems and nonequilibrium processes: an overview

“…Some of the most well-known nanocomposites are superlattices [93], in which the particles are distributed in a spatially ordered pattern, and the nanoparticles may be so small as to behave as quantum dots [94][95][96][97][98]. In metals and semiconductors, where electrons and holes also contribute to thermal conductivity, superlattices may be designed in such a way to strongly reduce phonon transport without reducing electron transport, because of the widely different values of phonon and electron wavelengths.…”