Thermal conductivity of GeTe/Sb2Te3 superlattices measured by coherent phonon spectroscopy

Abstract

We report on evaluation of lattice thermal conductivity of GeTe/Sb 2 Te 3 superlattice (SL) by using femtosecond coherent phonon spectroscopy at various lattice temperatures. The time-resolved transient reflectivity obtained in amorphous and crystalline GeTe/Sb 2 Te 3 SL films exhibits the coherent A 1 optical modes at terahertz (THz) frequencies with picoseconds dephasing time. Based on the Debye theory, we calculate the lattice thermal conductivity, including scattering by grain boundary and point defect, umklapp process, and phonon resonant scattering. The results indicate that the thermal conductivity in amorphous SL is less temperature dependent, being attributed to dominant phonon-defect scattering.

Phase‐Change Superlattice Materials toward Low Power Consumption and High Density Data Storage: Microscopic Picture, Working Principles, and Optimization

“…Therefore, Simpson et al argued that thermal conductivity cannot explain the low power consumption of SET process for IPCM. For SET state, the thermal conductivity of GST‐SL measured by coherent phonon spectroscopy was about 1.9 W m −1 K −1 , which is comparable with that of hexagonal GST (1.6 W m −1 K −1 ) but is much larger than that of rock‐salt GST (0.5 W m −1 K −1 ) . So, the thermal conductivity also cannot explain the low power consumption of RESET process for GST‐SL.…”

Thermoelectric and Thermal Properties of a (GeTe)2/Sb2Te3 Interfacial Phase‐Change Memory Device

“…In this study, we adopted the Callaway model [ 36 ] to represent .where we omitted the direction ( p ) dependence of the function for simplicity. We took parameter B from the literature, [ 37 ] whereas it is possible to evaluate B by first‐principle calculations or molecular dynamics simulations. is the Debye temperature averaged over all atoms whose atomic species is the same as for atom J .…”

“…However, should approach the intrinsic lattice thermal conductivity with increasing l and . Several groups have reported the lattice thermal conductivity of the GST‐SL film or bulk via experiments [ 37,43–46 ] as well as first‐principle calculations. [ 41 ] Hence, it is interesting to compare our with these experimental and theoretical studies.…”

“…0. Several groups have reported the lattice thermal conductivity of the GST-SL film or bulk via experiments [37,[43][44][45][46] as well as first-principle calculations. [41] Hence, it is interesting to compare our κ RSL lat with these experimental and theoretical studies.…”

Ultrafast dynamics of coherent optical phonons in GeTe/Sb2Te3 superlattices: thermal conductivity and coherent control

“…5, comparing the thermal conductivity obtained for the SL films in different phases, we found that the thermal conductivity in a-GeTe/Sb 2 Te 3 SL films is less temperature dependent, being due to dominant contribution from the phonon-defect scattering. On the contrary, in the crystalline phase thermal conductivity is strongly temperature dependent 31 , being attributed to significant contribution from umklapp and phonon resonant scatterings, both of which are related to the phonon dispersion curves and therefore they are significantly temperature dependent 24 . We note further that the thermal conductivity obtained in the SL films is high compared to the conventional GST alloy films; κ ≈ 0.2 Wm -1 K -1 for the amorphous and κ ≈ 0.4 Wm -1 K -1 for the crystalline (cubic) phases 9 .…”