Controllable ion beam deposition of Bi2Te3 thin films for flexible thermoelectric microdevices

This work investigates the ion-beam deposition (IBD) of Bi₂Te₃ thin films on flexible PET substrates, evaluating their integration into planar micro-thermoelectric generators (µ-TEGs). Ion-beam voltage ( V Beam = 600–1000 V is systematically varied to control growth kinetics, stoichiometry, structural order, and thermoelectric (TE) performance. Increasing V Beam promotes Te deficiency and Bi-rich phases with reduced crystallinity and enhanced lattice disorder, as confirmed by XRD, Raman spectroscopy, and EDS. These structural changes correlate with a non-monotonic evolution of the Seebeck coefficient and electrical conductivity, yielding an optimal power factor of ∼180 µW·m⁻¹ ·K⁻² at 700 V. Carrier concentration analysis (n ≈ 8 × 10 ¹⁹ cm⁻³) and a Mott-based estimate of the Fermi level ( E C − E F ≈ 11 meV) confirm degenerate n-type transport driven by Te depletion. The optimized films were implemented in flexible µ-TEGs fabricated by two-step photolithography, achieving 0.1400 ± 0.0075 mV·K⁻¹ and an output power density of 56 µW·cm⁻² under ΔT = 20 K. Finite element simulations corroborate the measured electrothermal behavior and reveal a low contact resistance ( R c ≈ 10⁻⁴ Ω·m²), a contact resistance within the range reported for thin-film thermoelectric interfaces. Overall, this study identifies a narrow processing window for obtaining functional Bi₂Te₃ films on PET and validates room-temperature IBD as a viable route for scalable fabrication of flexible TE devices.