Improved thermoelectric properties in Zn0.94Al0.06Ox films caused by oxygen defects via oxygen pressure

Al-doped ZnO films (Zn0.94Al0.06Ox) can be fabricated by thermal oxidation of evaporated metallic Zn-Al film. Oxygen defects were strongly related to oxygen pressure at a given temperature (500 °C) and duration (3 h). Under oxygen pressure of 0.021 MPa (O2-0.021 MPa), the main component was the Zn phase. Zn0.94Al0.06Ox films were formed under oxygen pressure of 0.1 MPa and 0.12 MPa, with the conductivity and Seebeck coefficient improving simultaneously with increased oxygen pressure. The flat particles of the O2-0.12 MPa film weakened the electron scattering, leading to increased conductivity. Furthermore, the decrease in oxygen vacancies caused by the higher oxygen pressure increased the Seebeck coefficient. As a result, the power factor of the O2-0.12 MPa film was about 30 times greater than that of the O2-0.1 MPa film, characterized by an increasing content of singly ionised oxygen.