Vapor Annealing as a Post-Processing Technique to Control Carrier Concentrations of Bi2Te3 Thin Films
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This article demonstrates that carrier concentrations in bismuth telluride films can be controlled through annealing in controlled vapor pressures of tellurium. For the bismuth telluride source with a small excess of tellurium, all the films reached a steady state carrier concentration of 4 × 1019 carriers/cm3 with Seebeck coefficients of −170 μV K−1. For temperatures below 300°C and for film thicknesses of 0.4 μm or less, the rate-limiting step in reaching a steady state for the carrier concentration appeared to be the mass transport of tellurium through the gas phase. At higher temperatures, with the resulting higher pressures of tellurium or for thicker films, it was expected that mass transport through the solid would become rate limiting. The mobility also changed with annealing, but at a rate different from that of the carrier concentration, perhaps as a consequence of the non-equilibrium concentration of defects trapped in the films studied by the low temperature synthesis approach.
KeywordsElectronic properties thermoelectric materials thin films
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This work was supported by the Office of Naval Research (N0014-07-1-0358). Clay Mortensen acknowledges support from an Integrative Graduate Education and Research Traineeship (IGERT) fellowship from the National Science Foundation, grant DGE-0549503.
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