Point defect-driven switching of conductivity type in Bi₂Te₃ films prepared by atomic layer deposition

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Bismuth telluride (Bi$_{2}$Te$_{3}$) is crucial for thin-film thermoelectric devices.
• Atomic Layer Deposition (ALD) enables precise nanoscale film fabrication.
• Limited reports exist on ALD synthesis of Bi$_{2}$Te$_{3}$ due to precursor challenges.

Purpose of the Study:

• To investigate the ALD synthesis of intrinsic Bi$_{2}$Te$_{3}$ films.
• To explore the influence of SiO$_{2}$ substrate thickness on film crystallinity and thermoelectric properties.
• To elucidate the mechanism of N-to-P type conversion during thermal cycling.

Main Methods:

• Fabrication of Bi$_{2}$Te$_{3}$ films via ALD with varying cycle counts (50-600).
• Deposition on SiO$_{2}$ substrates of different thicknesses.
• Characterization of film crystallinity, point defects, and thermoelectric performance.

Main Results:

• Successfully deposited Bi$_{2}$Te$_{3}$ films (<22 nm) using ALD.
• SiO$_{2}$ thickness impacts Bi$_{2}$Te$_{3}$ crystallinity, affecting point defects and enabling N/P type conversion.
• Achieved room temperature carrier concentration ~10$^{20}$ cm$^{-3}$ and a max power factor of 24.727 μW cm$^{-1}$ K$^{-2}$ at 453 K.

Conclusions:

• Nanoscale crystallinity differences significantly alter thermoelectric properties of Bi$_{2}$Te$_{3}$ thin films.
• ALD offers a viable route for fabricating tunable thermoelectric Bi$_{2}$Te$_{3}$ films.
• Understanding the transformation mechanism is key for optimizing thermoelectric device performance.