Bismuth Telluride Based Co-evaporated Thermoelectric Thin Films: Technology, Characterization and Optimization
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Thermoelectric (TE) materials have been widely investigated and used in a variety of systems such as solid-state coolers, infrared detectors, and power generators, by converting a temperature difference into electrical voltage or vice versa. Integration of TE thin films in micro-scale systems offers advantages such as integration, size, and weight for many new applications. In order to provide design flexibility for thermoelectric microsystems, high-quality TE thin films with good adhesion and uniformity are needed on a variety of substrates. However, the choice of substrate will affect film adhesion, stress, and optimal co-evaporation conditions. Motivated by the applications of TE materials in micro-systems, the goal of this dissertation is to investigate the technology and characterizations of high quality co-evaporated BiTe-based thin films on various substrates. Thermal evaporation is an attractive thin film deposition technique because of its relative simplicity, reproducibility, ease of process control, and high throughput. This work introduces co-evaporation as an effective and low-cost technique for development of Telluride-base ternary thin films. The characterization results show that the grain size, crystal structure, composition, and TE properties of thin films depend strongly on the co-evaporation process conditions including substrate material, substrate temperature during deposition, and elemental flux ratios.