Correlating thermoelectric (Bi,Sb)2Te3 film electric transport properties with microstructure

Abstract

The room temperature electronic transport properties of 1 μm thick Bi0.4Sb1.6Te3 (BST) films correlate with overall microstructural quality. Films with homogeneous composition are deposited onto fused silica substrates, capped with SiN to prevent both oxidation and Te loss, and postannealed to temperatures ranging from 200 to 450 °C. BST grain sizes and (00l) orientations improve dramatically with annealing to 375 °C, with smaller increases to 450 °C. Tiny few-nanometer-sized voids in the as-deposited film grain boundaries coalesce into larger void sizes up to 300 nm with annealing to 350 °C; the smallest voids continue coalescing with annealing to 450 °C. These voids are decorated with few-nanometer-sized Sb clusters that increase in number with increasing annealing temperatures, reducing the Sb content of the remaining BST film matrix. Resistivity decreases linearly with increasing temperature over the entire range studied, consistent with improving crystalline quality. The Seebeck coefficient also improves with crystalline quality to 350 °C, above which void coalescence and reduced Sb content from the BST matrix correlate with a decrease in the Seebeck coefficient. Nevertheless, a plateau exists for an optimal power factor between 350 and 450 °C, implying thermal stability to higher temperatures than previously reported.

The effect of metal–insulator interface interactions on electrical transport in granular metals

“…Nominally 100 nm thick GM films were deposited and then sputtercoated in situ with a 10 nm thick SiN x capping layer to prevent oxidation of the surface metal islands. SiN x is an oxidation barrier [58,59]. The VDP measurement samples were then transferred to a separate high vacuum chamber where 2 × 2 mm 2 Ti/Au corner electrodes were defined with a shadow mask.…”