Reduction in thermal conductivity of Sb₂Te phase-change material by scandium/yttrium doping

Binary Sb₂Te is considered as a potential recording material for phase-change memory due to its higher crystallization speed than the widely investigated ternary Ge-Sb-Te alloys. To further improve the performance of Sb₂Te, various dopants such as scandium (Sc) have been explored. Yet, the thermal conductivity of the pristine and doped Sb₂Te is unknown, even though the thermal conductivity (κ) is an essential parameter for phase change memory devices as thermal conductivity determines the exchange of energy with surroundings and heat transport in the SET/RESET process. In this work, by means of ab initio calculations, we have calculated the thermal conductivity of Sb₂Te, scandium (Sc)-doped and yttrium (Y)-doped Sb₂Te. The calculated lattice thermal conductivity values at 300 K are 3.76 Wm⁻¹K⁻¹, 3.22 Wm⁻¹K⁻¹ and 3.35 Wm⁻¹K⁻¹ for pristine Sb₂Te, Sc-doped Sb₂Te, and Y-doped Sb₂Te, respectively, showing a reduction in lattice thermal conductivity by doping. Further analysis of the electron localization function and Bader charge distribution suggest that the increased bonding strength of the dopants with the surrounding atoms contributes to the reduction in lattice thermal conductivity of the doped Sb₂Te. On the other hand, the electronic thermal conductivity of Sb₂Te should also decrease due to the metal to semiconductor transition by Sc/Y doping as analyzed by the calculated density of states. Overall, the thermal conductivity of Sb₂Te decreases to some extent by doping Sc and Y, which can lower the energy consumption and improve the efficiency of energy utilization in the data SET/RESET process and is thus desirable for phase-change memory devices.