R&D: Temperature-Dependent Thermal Conductivity of Ge2Sb2Te5 Polymorphs from 80 to 500K

Journal of Applied Physics has published an article written by Qinshu Li, Tsinghua-Berkeley Shenzhen Institute, Tsinghua University, Shenzhen 518055, China, Or Levit, Eilam Yalon, Viterbi Faculty of Electrical and Computer Engineering, Technion-Israel Institute of Technology, Haifa 3200003, Israel, and Bo Sun, Tsinghua-Berkeley Shenzhen Institute, Tsinghua University, Shenzhen 518055, China, and Tsinghua Shenzhen International Graduate School and Guangdong Provincial Key Laboratory of Thermal Management Engineering and Materials, Shenzhen 518055, China.

Abstract: “We report the thermal conductivity of amorphous, cubic, and hexagonal Ge2Sb2Te5 using time-domain thermoreflectance from 80 to 500 K. The measured thermal conductivities are 0.20 W m−1 K−1 for amorphous Ge2Sb2Te5, 0.63 W m−1 K−1 for the cubic phase, and 1.45 W m−1 K−1 for the hexagonal phase at room temperature. For amorphous Ge2Sb2Te5, the thermal conductivity increases monotonically with temperature when T < 300 K, showing a typical glass-like temperature dependence, and increases dramatically after heating up to 435 K due to partial crystallization to the cubic phase. For hexagonal Ge2Sb2Te5, electronic contribution to thermal conductivity is significant. The lattice thermal conductivity of the hexagonal phase shows a relatively low value of 0.47 W m−1 K−1 at room temperature and has a temperature dependence of T−1 when T > 100 K, suggesting that phonon–phonon scattering dominates its lattice thermal conductivity. Although cubic Ge2Sb2Te5 has a similar grain size to hexagonal Ge2Sb2Te5, its thermal conductivity shows a glass-like trend like that of the amorphous phase, indicating a high concentration of vacancies that strongly scatter heat-carrying phonons. These thermal transport mechanisms of Ge2Sb2Te5 polymorphs help improve the thermal design of phase change memory devices for more energy-efficient non-volatile memory.“