Addressing the Electronegativity Impact on the Thermal-Electrical Properties of Doped ZnO Thermoelectric Films

The thermoelectric properties of undoped ZnO (ZnO), Mg-doped ZnO (MZO), Al-doped ZnO (AZO), and Ga-doped ZnO (GZO) films were addressed in terms of the electronegativity difference (Delta chi). A smaller Delta chi not only increases bond covalency and larger orbital overlap but also reduces intrinsic defects, leading to higher electrical conduction and larger carrier mobility observed in AZO and GZO films. In contrast, the MZO films with the largest Delta chi, which enhance intrinsic defects (oxygen vacancies, etc.) or potential barriers at grain boundaries, reduce bond covalency, or increase bond ionicity, result in the lowest electrical conductivity and carrier mobility. The power factor PF values are 93, 27, 49, and 148 mu W m-1 K-2 for the ZnO, MZO, AZO, and GZO films, respectively. Films having atoms with smaller Delta chi values achieve the larger PF value. As a result, replacing Zn sites with dopants of larger electronegativity or small electronegativity difference is an indicator for enhancing the thermoelectric properties of ZnO materials.