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

Germanium tellurides and their pseudobinary compounds offer interesting properties that are important in thermoelectric and phase-change applications. Despite being a class of materials under scrutiny since its discovery, unique properties and functionalities have kept on emerging in recent years. In this work, we observed another unique property of Ge–Sb–Te (GST) thin film that can be beneficial in its development for thermoelectric applications. A rapid heating and quenching process of the GST film resulted in a metastable rock-salt cubic structure, exhibiting a unique electronic-transition-like behavior. Above the transition temperature at 150 °C, we observed a temperature-induced band modulation, corroborated with changes in its effective mass and valence band position that leads to favorable electronic and thermoelectric properties. Charge transfer between Sb and Te occurred, accompanied by a distorted cubic-to-cubic structural change. The interplay of the electronic and lattice structure born out of the composition and phase of the Ge–Sb–Te thin film opened up the possibility for the future of thermoelectric devices.