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

Abstract

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 (T-s) between 200 and 350 degrees 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 similar to 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 degrees C, resulting in enhanced carrier mobility (mu) and electrical conductivity (sigma) 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 degrees C to layered-hexagonal platelets (L-HPs) or super-layered flakes (S-LFs) at T-s of 300-350 degrees C. Films that were grown at 300 degrees C and 40 Pa and contained highly c-axis oriented L-HPs possessed the highest power factor (PF =S-2 sigma), which reached 5.54 mu W cm(-1) K-2, where S=75.8 mu V/K and sigma = 963.8 S cm(-1). (C) 2013 Elsevier B.V. All rights reserved.