Thermoelectric properties of c-GeSb0.75Te0.5 to h-GeSbTe0.5 thin films through annealing treatment effects

Germanium-Antimony-Tellurium (Ge-Sb-Te) thin films were deposited on silicon wafers with 1-mu m silicon dioxide (SiO2/Si) by pulsed dc magnetron sputtering from a 99.99% GeSbTe target of 1:1:1 ratio at ambient temperature. The samples were annealed at 573, 623, 673, and 723 K for 3600 s in a vacuum state. The effects of the annealing treatment on phase identification, atomic composition, morphology and film thickness, carrier concentration, mobility, and Seebeck coefficient of the Ge-Sb-Te samples have been investigated by grazing-incidence X-ray diffraction, auger electron spectroscopy, field-emission scanning electron microscopy, Hall-effect measurements, and steady state method, respectively. The results demonstrated that the as-deposited Ge-Sb-Te sample was amorphous. Atomic composition of as-deposited and annealed films at 573 K and 623 K were GeSb0.75Te0.5 while annealed films at 673 K and 723 K were GeSbTe0.5 due to Sb-rich GeSb0.75Te0.5. The samples annealed at 573 K and 623 K showed the crystal phases of cubic structure (c-GeSb0.75Te0.5) into hexagonal structure (h-GeSbTe0.5) after annealing at 673 K and 723 K. The study demonstrated the insulating condition from the as-deposited Ge-Sb-Te film, and the changes towards the thermoelectric properties from the annealing treatments. The Ge-Sb-Te films annealed at 673 K yielded excellent thermoelectric properties with the electrical resistivity, Seebeck coefficient, and power factor at approximately 1.45 x 10(-5) Omega m, 71.07 mu V K-1, and 3.48 x 10(-4) Wm(-1) K-2, respectively. (C) 2015 Elsevier B.V. All rights reserved.