Thermoelectric properties of bismuth-selenide films with controlled morphology and texture grown using pulsed laser deposition

Polycrystalline, thermoelectric thin films of bismuth selenide (Bi2Se3) were grown on SiO2/Si (1 1 1) substrates, using pulsed laser deposition (PLD). Bi2Se3 films with highly c-axis-oriented and controlled textures were fabricated by maintaining the helium gas pressure (P) between 0.7 and 173 Pa and the substrate temperature (Ts) between 200 and 350 °C. The carrier concentration (n) of films decreased with increasing P, which was attributed to the increase of Se concentration from Se deficiency (P ≤ 6.7 Pa) to stoichiometry to slight Se enrichment (P ≥ 40 Pa). The Seebeck coefficient (S) was enhanced considerably because of the reduction in n, following the S ∼ n−2/3 relation approximately. The average grain size increased from approximately 100 to 500 nm when Ts was raised from 200 to 350 °C, resulting in enhanced carrier mobility (μ) and electrical conductivity (σ) and a reduced full width at half maximum of (0 0 6) peaks. The shape of grains transformed from rice-like at Ts of 200-250 °C to layered-hexagonal platelets (L-HPs) or super-layered flakes (S-LFs) at Ts of 300-350 °C. Films that were grown at 300 °C and 40 Pa and contained highly c-axis oriented L-HPs possessed the highest power factor (PF = S2σ), which reached 5.54 μW cm−1 K−2, where S = 75.8 μV/K and σ = 963.8 S cm−1.