Tuning network topology and vibrational mode localization to achieve ultralow thermal conductivity in amorphous chalcogenides

Amorphous chalcogenide alloys are key materials for data storage and energy scavenging applications due to their large non-linearities in optical and electrical properties as well as low vibrational thermal conductivities. Here, we report on a mechanism to suppress the thermal transport in a representative amorphous chalcogenide system, silicon telluride (SiTe), by nearly an order of magnitude via systematically tailoring the cross-linking network among the atoms. As such, we experimentally demonstrate that in fully dense amorphous SiTe the thermal conductivity can be reduced to as low as 0.10 ± 0.01 W m−1 K−1 for high tellurium content with a density nearly twice that of amorphous silicon. Using ab-initio simulations integrated with lattice dynamics, we attribute the ultralow thermal conductivity of SiTe to the suppressed contribution of extended modes of vibration, namely propagons and diffusons. This leads to a large shift in the mobility edge - a factor of five - towards lower frequency and localization of nearly 42% of the modes. This localization is the result of reductions in coordination number and a transition from over-constrained to under-constrained atomic network.

Ultralow thermal conductivity via topological network control of vibrational localization in amorphous chalcogenides

Amorphous chalcogenide alloys are key materials for data storage and energy scavenging applications due to their large non-linearities in optical and electrical properties as well as low vibrational thermal conductivities. Here, we report on a mechanism to suppress the thermal transport in a representative amorphous chalcogenide system, silicon telluride (SiTe), by nearly an order of magnitude via systematically tailoring the cross-linking network among the atoms. As such, we experimentally demonstrate that in fully dense amorphous SiTe the thermal conductivity can be reduced to as low as 0.1 ± 0.01 W/m/K for high tellurium content with a density nearly twice that of amorphous silicon. Using ab-initio simulations integrated with lattice dynamics, we attribute the ultralow thermal conductivity of SiTe to the suppressed contribution of extended modes of vibration, namely propagons and diffusons. This leads to a large shift in the mobility edge - a factor of five - towards lower frequency and localization of nearly 42% of the modes. This localization is the result of reductions in coordination number and a transition from over-constrained to underconstrained atomic network.

Оптические свойства фазопеременных материалов системы германий--сурьма-теллур составов Ge-=SUB=-14-=/SUB=-Sb-=SUB=-29-=/SUB=-Te-=SUB=-57-=/SUB=- и Ge-=SUB=-15-=/SUB=-Sb-=SUB=-15-=/SUB=-Te-=SUB=-70-=/SUB=- в дальнем инфракрасном диапазоне

Infrared absorption spectra of chalcogenide alloys of the GST system with the compositions Ge14Sb29Te57 and Ge15Sb15Te70 in the amorphous and crystalline state were measured and analyzed in the range of 20 – 400 cm– 1 (0.6 – 12 THz) at room temperature. Absorption at these frequencies is due to the manifestation of correlated torsional vibrations of structural units of the amorphous alloy and phonon modes of the crystal. The performed assignment of absorption bands and the revealed differences in the IR spectra make it possible to more confidently represent the possible molecular mechanism of reversible amorphous-crystalline transformations in the studied phase-changing materials

PE-ALD of Ge1-xSx amorphous chalcogenide alloys for OTS applications

Three-dimensional (3D) cross-point (X-point) technology, including amorphous chalcogenide-based ovonic threshold switching (OTS) selectors, is bringing new changes to the memory hierarchy for high-performance computing systems. To prepare for future 3D...