A study on the thermoelectric properties of ALD-grown aluminum-doped tin oxide with respect to nanostructure modulations

Abstract

The thermoelectric properties of aluminum-doped tin oxide (ATO) thin films synthesized by thermal atomic layer deposition (ALD) were studied with respect to the aluminum concentration. The overall aluminum content in each layer was modulated by adjusting the relative number of tin oxide (SnO2) and aluminum oxide (Al2O3) growth cycles, where a sequential process involving n cycles of SnO2 growth followed by 1 cycle of Al2O3 deposition was performed (building up a super-cycle). The electrical conductivity (620 S/cm), free carrier concentration (1.23x10(21) cm(-3)), and power factor (0.49 mW/K(2)m) increase until their maximum values are reached when the Al content is approximately 1.50 at% of the cations, and decrease as more Al is added in. On the other hand, the Seebeck coefficient decreases monotonically as the Al content increases up to about 2.88 at %, and begins to increase with further Al doping. Here the thermoelectric efficiency is therefore determined primarily by the free carrier concentration, while the Seebeck coefficient appears to be influenced by the overall crystal structure.