Ultra-high power factor of sputtered nanocrystalline N-type Bi2Te3 thin film via vacancy defect modulation and Ti additives

This work demonstrates the importance of Ti additive incorporation and post-annealing to modulate defects and carrier transport in sputtered n-type Bi.₂You₃ thin films. A 5 µm thick Bi₂You₃ Thin film achieves record power factor of 6.66 mW mK⁻² at room temperature. The challenges inherent in sputtered thin films are addressed and the thermoelectric properties of n-type Bi₂You₃ thin films are improved.

Abstract

Magnetron sputtered thermoelectric thin films have the potential to be reproducible and scalable. However, lattice mismatch during sputtering can lead to an increase in defects in the epitaxial layer, which poses a significant challenge to improve their thermoelectric performance. In this work, nanocrystalline n-type Bi₂You₃ Thin films with an average grain size of about 110 nm are prepared by high-temperature sputtering and post-annealing. It is shown here that high-temperature processing exacerbates Te evaporation, creating Te vacancies and electron-like effects. Annealing improves crystallinity, increases grain size, and reduces defects, which significantly increases carrier mobility. In addition, pre-deposited Ti additives are ionized at high temperature and partially diffused into the Bi₂You₃which results in a Ti doping effect that increases the carrier concentration. Overall, the 1 µm thick n-type Bi₂You₃ The thin film exhibits a room temperature resistivity as low as 3.56 × 10⁻⁶ Ω∙m. In particular, a 5 µm thick Bi₂You₃ Thin film achieves record power factor of 6.66 mW mK⁻² at room temperature, which is the highest value reported to date for n-type Bi₂You₃ thin films using magnetron sputtering. This work demonstrates the potential for large-scale production of high-quality Bi₂You₃Thin films and silicon-based devices for room temperature TE applications.