Thermoelectric behaviors of ZnO mesoporous thin films affected by strain induced from the different dopants radii (Al, Ga, and In)

This study considered effects from thermoelectric property changes due to mesoporous thin film ZnO lattice deformation through doping with various group III elements. The distorted hexagonal wurtzite structure occurred in the ZnO thin film due to ion size differences between Zn and other doping elements. These strains cause distortion, resulting in reduced mobility because they inhibit grain growth and reduce crystallinity. Al doping induced the largest strain since it represented the largest ionic radius difference from Zn, whereas strain differences between Ga and In doped ZnO were almost negligible. In is larger than Zn, whereas Al and Ga dopants have a smaller atomic radius. Thus, carrier concentration for the smaller ion was 18%–26% higher than for the larger ion, and electroconductivity and carrier concentration increased 2–3.5- and 5–10-fold, respectively, with increasing dopant concentration, regardless of the doping element. Ga was the best candidate among the group III elements for doping a ZnO thin film, achieving the highest power factor of 8.01 at 323 K. We verified that thermoelectric properties could be improved by controlling dopant concentration, being influenced from inducing crystal lattice deformation through ion radius differences between the dopant and Zn.