Abstract
The effect of grain boundary potential scattering on thermoelectric properties of Bi0.5Sb1.5Te3 thin films has been investigated. Bi0.5Sb1.5Te3 is known to be the best p-type thermoelectric material at the room temperature regime. In this study, the Bi0.5Sb1.5Te3 thin films of various grain sizes were deposited at different substrate temperatures by the magnetron sputter deposition method. As the deposition temperature increases from room temperature to 200 ºC, the grain size of the sputtered Bi0.5Sb1.5Te3 thin films increase from 25nm to 100nm. The sputtered thin film with the smallest grain size has a very high Seebeck coefficient of 280 μV/K, which is 50% higher than that of the film of 100 nm in grain size. By comparing the measured carrier concentration, mobility, resistivity with the theoretical predictions from the carrier transport model, it is suggested that the enhancement of Seebeck coefficient for the sputtered Bi0.5Sb1.5Te3 thin films is mainly attributed to the effect grain boundary potential scattering. Since the as-deposited Bi0.5Sb1.5Te3 thin films have high electrical resistivity, two different thermal treatments, high temperature/short duration and low temperature/long duration, have been employed to reduce the resistivity of the sputtered Bi0.5Sb1.5Te3 thin films. It is found that the Bi0.5Sb1.5Te3 thin films has the lowest resistivity of 6.3mΩ-cm and a moderately reduced Seebeck coefficient of 210μV/K, leading to the highest power factor of 7 10-4W/m-K2 after annealing at 225 ºC for 5 minutes.