Thermoelectric properties of nanocrystalline Bi3Se2Te thin films grown using pulsed laser deposition

This study reports the material and thermoelectric properties of n-type nanocrystalline Bi-Se-Te thin films grown using pulse laser deposition (PLD) with a Bi2Se2Te single crystal as the target. In order to optimize the transport and thermoelectric properties, Bi-Se-Te thin films are fabricated by maintaining the substrate temperature (TS) between 200 and 350 °C and a helium gas pressure (PHe) from 0.027 to 86.7 Pa. Unlike the target, all deposited films unexpectedly exhibit Bi3Se2Te phase with highly c-axis orientation, because of the high re-evaporation rates of Se and Te at the elevated TS ≥ 200 °C. The estimated grain (crystalline) size ranges between 18.4 and 39.4 nm, and this monotonically increases as TS increases. The Bi3Se2Te films demonstrate excellent electrical conductivities owning to the high carrier concentration in the order of 1020 cm−3. A window of deposition conditions for high thermoelectric power factors (PF) is TS of 250-350 °C and PHe of 40 Pa. The optimal PF is 8.3 μW/cmK2 for the Bi3Se2Te film prepared at 250 °C and 40 Pa.