Electronic and Thermal Properties of GeTe/Sb2Te3 Superlattices by ab initio Approach: Impact of Van der Walls Gaps on Vertical Lattice Thermal Conductivity

In the last decade, several works have focused on exploring the material and electrical properties of GeTe/Sb2Te3 superlattices (SLs) in particular because of some first device implementations demonstrating interesting performances such as fast switching speed, low energy consumption, and non-volatility. However, the switching mechanism in such SL-based devices remains under debate. In this work, we investigate the prototype GeTe/Sb2Te3 SLs, to analyze fundamentally their electronic and thermal properties by ab initio methods. We find that the resistive contrast is small among the different phases of GeTe/Sb2Te3 because of a small electronic gap (about 0:1 eV) and a consequent semi-metallic-like behavior. At the same time the out-of-plane lattice thermal conductivity is rather small, while varying up to four times among the different phases, from 0:11 to 0:45 W/mK, intimately related to the number of Van der Waals (VdW) gaps in a unit block. Such findings confirm the importance of the thermal improvement achievable in GeTe/Sb2Te3 super-lattices devices, highlighting the impact of the material stacking and the role of VdW gaps on the thermal engineering of the Phase-Change Memory cell.