Synthesis and Characterization of Bismuth Telluride Bi2Te3 Thin Films for Thermoelectric Cooler

Abstract

Thermoelectric (TE) materials have been widely investigated and used in a variety of systems such as solid-state coolers, infrared detectors, and power generators. 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. Motivated by the applications of TE materials in microsystems, the goal of this dissertation is to explore the technology and characterization of co-evaporated high quality (Bi,Sb)Te-based thin films on various substrates. newlineThermal evaporation is an attractive thin film deposition technique because of its relative simplicity, reproducibility, ease of process control, and high throughput. Characterization techniques are applied to a variety of TE films in order to enhance physical understanding of the effects of deposition conditions, substrate material/crystalline, and substrate preparation on film properties. This dissertation shows that the grain size, composition, and TE properties of thin films depend strongly on the co-evaporation process conditions including substrate material, deposition substrate temperature, and elemental flux ratio. Our results show that maximum power factors are achieved on Poly-Si and Kapton® substrates at Tsub= 270 °C for n-type Bi2Te3 films, and on oxide and poly-Si substrates at Tsub= 250°C for p-type Sb2Te3 films. The optimum (Bi,Sb)Te-based binary films have tellurium atomic percentage of about 60%. newlineThis work moves beyond co-evaporation of binary alloys towards advanced thermoelectric films of ternary alloys. It demonstrates co-evaporation as a low-cost process for the deposition of telluride-based ternary films for the first time. newline