Berlin 2008 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 31: Poster II

HL 31.52: Poster

Tuesday, February 26, 2008, 16:30–19:00, Poster D

Structural Change and Power Factor Enhancement of Thermoelectric p-type Films — •Katrin Rothe¹, Matthias Stordeur², Hartmut Leipner¹, Frank Heyroth¹, and Bernd Engers² — ¹Interdisziplinäres Zentrum für Materialwissenschaften, Martin-Luther-Universität 06099 Halle — ²angaris GmbH, Heinrich-Damerow-Str. 1, 06120 Halle

By sputter-deposition thin films of the thermoelectric effective p-type compound semiconductor (Bi_0.15 Sb_0.85)₂ Te₃ were prepared. For the first time a distinct increase of the electrical conductivity σ was observed after heating of the as-deposited films and afterwards cooling. For the enlightenment of this typical behavior, which seems to be similar found for phase change materials consisting of (Ge, Sb, Te)-alloys, also the Seebeck (S) and the Hall coefficient were measured. It was established that the increase of the electrical conductivity is not connected with an expected decrease of the Seebeck coefficient, because the charge carrier density is reduced but at the same time the hole mobility is increasing. Corresponding analytical investigations by XRD, EDX, and REM shows that besides a grain growth in the polycrystalline films a Te-rich phase appears after the heat treatment. The increase of the electrical conductivity at nearly unchanged Seebeck coefficient can be exploited for the enhancement of the film power factor (S²σ). This is important for the efficiency of thermoelectric thin films devices as miniaturized coolers, generators, and sensors. Nevertheless for a quantitative interpretation of the presented new experimental results further investigations and theoretical considerations are required.