Achieving Extraordinary Power Factors in GeTe Epitaxial Films through Carrier Transport Engineering

GeTe-based films have attracted tremendous attention from the thermoelectric community owing to their excellent thermoelectric performance. It is vital to reduce the hole density and maintain a high carrier mobility for GeTe films; however, this remains a significant challenge. To overcome this drawback, we succeeded in fabricating high-crystalline quality GeTe-based films and remarkably improve their electrical properties using molecular beam epitaxy under a low substrate temperature and optimized Te/GeTe flux ratios. The Bi2Te3/GeTe double-layer buffer facilitated the reliable fabrication of high-quality GeTe films. The hole density and carrier mobility were synergistically optimized under a relatively low substrate temperature of 503 K and Te/GeTe flux ratio of 0.25/1 that suppress the formation of Ge vacancies, as well as a trace amount of Sb2Te3 incorporation that introduces SbTe substitutional defects. The best (GeTe)24/(Sb2Te3)0.25 film acquires a very low hole density of 2.57 × 1020 cm–3 and, simultaneously, a high carrier mobility of 96.53 cm2 V–1 s–1, which leads to an extraordinary power factor of 3.36 mW m–1 K–2 at room temperature as well as an average power factor of 4.15 mW m–1K–2 within 300–475 K, outperforming the values of GeTe from previous reports. This work provides valuable insights for fabricating high-performance GeTe-based films to promote their future applications near room temperature.