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.