Uncovering Thermal and Electrical Properties of Sb2Te3/GeTe Superlattice Films

TL;DR

This study characterizes the thermal and electrical transport properties of Sb2Te3/GeTe superlattice films, revealing significant reductions in thermal conductivity and strong electrical anisotropy, advancing low-power phase change memory design.

Contribution

It provides detailed experimental insights into the thermal and electrical transport mechanisms in Sb2Te3/GeTe superlattices, including phonon coherence and interface effects, which were not previously well understood.

Findings

Up to 4X reduction in thermal conductivity compared to GST.

Observation of phonon coherence transition from wave-like to particle-like.

Electrical resistivity anisotropy of about 2000X between in-plane and cross-plane directions.

Abstract

Superlattice-like phase change memory (SL-PCM) promises lower switching current than conventional PCM based on Ge2Sb2Te5 (GST). However, a fundamental understanding of SL-PCM requires detailed characterization of the interfaces within such a SL. Here, we explore the electrical and thermal transport of SLs with deposited Sb2Te3 and GeTe alternating layers of various thicknesses. We find up to ~4X reduction of the effective cross-plane thermal conductivity of the SL stack (as-deposited polycrystalline) compared to polycrystalline GST (as-deposited amorphous and later annealed) due to the thermal interface resistances within the SL. Thermal measurements with varying periods of our SLs show a signature of phonon coherence with a transition from wave-like to particle-like phonon transport, further described by our modeling. Electrical resistivity measurements of such SLs reveal strong anisotropy (~2000X) between the in-plane and cross-plane directions due to the weakly interacting van der Waals gaps. This work uncovers electro-thermal transport in SLs based on Sb2Te3 and GeTe, for improved design of low-power PCM.