Enhanced Power Factor through Valence Band Convergence and High Mobility Retention in MnTe-Alloyed GeTe Films

The multiple valence band edges of GeTe provide an important degree of freedom for optimizing thermoelectric transport properties. However, conventional multielement co-doping strategies employed to achieve valence band convergence often introduce additional carrier scattering centers, leading to substantial mobility degradation and limiting further improvement of thermoelectric performance. To address this challenge, MnTe alloying is applied to high-mobility GeTe films grown using an optimized epitaxial buffer layer structure, yielding (GeTe)x(MnTe)y films that exhibit valence band convergence while retaining relatively high carrier mobility. Dilute MnTe alloying effectively tailors the valence band structure of GeTe, enabling the optimization of carrier transport in the (GeTe)36(MnTe)0.5 film, which exhibits a Seebeck coefficient of 110.14 μVK–1, a hole concentration of 2.56 × 1020 cm–3, and a carrier mobility of 70.2 cm2V–1s–1. The balance between an enhanced Seebeck coefficient and relatively high carrier mobility results in a room-temperature power factor of 3.49 mWm–1K–2, surpassing values reported for GeTe-based bulk materials. This work demonstrates an effective strategy for mitigating the trade-off between a large Seebeck coefficient and high carrier mobility in GeTe, providing valuable insights into the development of GeTe-based thin films for potential near-room-temperature applications.