Improving the thermoelectric performance of metastable rock-salt GeTe-rich Ge-Sb-Te thin films through tuning of grain orientation and vacancies

Abstract

Phase‐change memory materials such as the pseudobinary GeTe‐Sb2Te3 compounds have recently gained attention for their good thermoelectric properties, which can be used for power‐generation/cooling applications. In this work, GeTe‐rich Ge–Sb–Te thin films deposited using a radio‐frequency magnetron sputtering method readily exhibit the metastable face‐centered cubic (FCC) phase at room temperature. This is in stark contrast to its bulk form, which only transforms to its FCC phase after a transition temperature of around 350 °C. Based on previous works, the FCC phase contributes to the superior thermoelectric properties of this material system. In this study, by decreasing the working deposition pressure, the preferred orientation of (200) plane is observed that translates to improved carrier mobility. Moreover, increasing the annealing temperature has been shown to decrease the carrier concentration due to Te deficiency, leading to a significant improvement in the Seebeck coefficient of the film. By combining these effects, an optimized thermoelectric power factor (21 μW/cm K2) was obtained at an operating temperature of 350 °C.

Origin of Band Modulation in GeTe-Rich Ge–Sb–Te Thin Film

“…Previously, we also have shown that the thermoelectric properties of GST in the thin-film form were tunable through morphological control and different from its bulk counterpart . Here, we further demonstrate that a nonequilibrium thermal treatment, in which the film was rapidly heated (at a rate of ∼50 °C/min) up to its decomposition temperature (∼550 °C) followed immediately by fast air-quenching, allowed us to obtain a nonstoichiometric GeTe-rich GST thin film.…”

Thermoelectric Materials and Applications: A Review

“…Chen et al [176] achieved a power factor value of 2 mW•m −1 •K −2 at 523 K testing GeTerich Ge-Sb-Te thin films annealed at 450 • C (for most self-powered devices 1 mW•m −1 •K −2 is enough [21,177]). In that case, they deposited the films on a silica substrate via radio frequency magnetron sputtering at room temperature; after annealing at 450 • C, the thin film thickness was around 338 nm.…”

The microstructure and electrical and optical properties of Ge–Cu–Te phase-change thin films

“…40 Chen et al have reported that the preferred orientation of the (200) plane in GeTe-rich Ge-Sb-Te thin films can improve carrier mobility. 41 In the current work, the grain orientation and GBCD of crystalline Ge-Cu-Te thin films are characterized using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) for the first time, with the aim to improve our understanding of the microstructural and textural evolutions of Ge-Cu-Te thin films. Furthermore, the impact of grain orientation evolution during annealing on electrical and optical properties was also studied.…”

“…40 Chen et al have reported that the preferred orientation of the (200) plane in GeTe-rich Ge–Sb–Te thin films can improve carrier mobility. 41…”