Structural and surface morphology of nanocystalline bismuth telluride thin films deposited using radio frequency magnetron sputtering

Abstract

Nanocrystalline Bi2Te3 thin film is a highly potential material to be used in semiconductor thermoelectric because of its refined and enhanced properties. The deposition and characterization of Bi2Te3 thin films are reported in this work. Films were deposited with substrate temperature ranging from 50 ºC to 150 ºC, argon flow rate from 5 cm3 min-1 to 25 cm3 min-1, deposition time from 300 s to 900 s and RF power from 50 W to 250 W. In-situ annealing and rapid cooling for thin film deposited under 100 ºC substrate temperature was performed. AFM topographyimages shows that Bi2Te3 thin films follow the Frank de Merwe deposition mode.The lowest surface roughnesses obtained were 0.35 nm, 0.02 nm, 0.11 nm and 0.06nm, at 150 ºC substrate temperature, 20 cm3 min-1 argon flow rate, 450 s deposition time and 50 W RF power, respectively. The smallest grain sizes obtained were 33.9nm, 19.91 nm, 37.99 nm and 14.27 nm which were deposited at 150 ºC substrate temperature, 25 cm3 min-1 argon flow rate, 450 s deposition time and at 50 W RF power, respectively. XRD analyses revealed that the thin films were in the form of polycrystalline structure. The largest nanocrystalline size was obtained at 900 sde position time while the smallest size was obtained at 125 ºC substrate temperature.In-situ annealing showed an improved grain size and surface roughness as annealing temperature increased. Rapid cooling successfully eliminated the worm-like dimeron the surface, improved grain size and area grain density. Great significant of structural and surface morphology was found as a function of deposition parameters,namely the substrate temperature, argon flow rate, deposition time and RF power.