Decisive Role of Initial Crystallinity in Spontaneously Forming High-Performance a-Ge/GeTe/a-Ge Sandwich Thermoelectric Films

Germanium telluride (GeTe) is a leading candidate for medium-temperature thermoelectric applications, but its practical deployment in thin-film devices is severely hindered by thermal instability caused by tellurium (Te) volatilization. While conventional strategies rely on elemental doping to mitigate this issue, this study demonstrates that the initial crystallinity of the as-deposited film is the decisive factor in determining structural evolution and device performance. Specific thermal processing produces a unique “ideal-glass-like” amorphous state that fundamentally alters the diffusion kinetics during operation. Unlike initially crystalline films that degrade due to void formation, these amorphous films undergo spontaneous self-organization into a robust a-Ge/GeTe/a-Ge sandwich structure. This architecture serves a dual function: the segregated amorphous Ge (a-Ge) layers act as self-passivating barriers to suppress Te volatilization and simultaneously serve as high-mobility conduction channels. Consequently, the optimized films achieve a 30% enhancement in power factor compared to conventional counterparts while maintaining excellent structural integrity. These findings establish a paradigm for designing maintenance-free, high-performance energy harvesters by leveraging initial microstructural engineering rather than complex compositional tuning.