Effect of substrate on thermoelectric properties of Al-doped ZnO thin films

We have prepared 2% Al doped ZnO (AZO) thin films on SrTiO₃ (STO) and Al₂O₃ substrates by Pulsed Laser Deposition technique at various deposition temperatures (T_dep = 300°C-600°C). Transport and thermoelectric properties of AZO thin films were studied in low temperature range (300 K-600 K). AZO/STO films present superior performance respect to AZO/Al₂O₃ films deposited at the same temperature, except for films deposited at 400°C. Best film is the fully c-axis oriented AZO/STO deposited at 300°C, which epitaxial strain and dislocation density are the lowest: electrical conductivity 310 S/cm, Seebeck coefficient -65 μV/K, and power factor 0.13 × 10^-3 W m^-1 K^-2 at 300 K. Its performance increases with temperature. For instance, power factor is enhanced up to 0.55 × 10 ^-3 W m^-1 K^-2 at 600 K, surpassing the best AZO film previously reported in literature.