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

Polycrystalline, thermoelectric thin films of bismuth selenide (Bi ₂ Se ₃ ) were grown on SiO ₂ /Si (1 1 1) substrates, using pulsed laser deposition (PLD). Bi ₂ Se ₃ 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 (T _s ) 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 T _s 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 T _s of 200-250 C to layered-hexagonal platelets (L-HPs) or super-layered flakes (S-LFs) at T _s 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 = S ² σ), which reached 5.54 μW cm ^-1 K ^-2 , where S = 75.8 μV/K and σ = 963.8 S cm ^-1 .