Thermoelectric properties of Al-doped ZnO: experiment and simulation

Advancement in doping other elements, such as Ce, Dy, Ni, Sb, In and Ga in ZnO^1], have stimulated great interest for high-temperature thermoelectric application. In this work, the effects of Al-doping in a ZnO system on the electronic structure and thermoelectric properties are presented, by experiment and calculation.Nanosized powders of Zn_1-xAl_xO (x=0, 0.01, 0.02, 0.03 and 0.06) were synthesized by hydrothermal method. From XRD results, all samples contain ZnO as the main phase and ZnAl₂O₄ (spinel phase) peaks were visible when Al additive concentrations were just 6 at%. The shape of the samples changed and the particle size decreased with increasing Al concentration. Seebeck coefficients, on the other hand, did not vary significantly. They were negative and the absolute values increased with temperature. However, the electrical resistivity decreased significantly for higher Al content.The electronic structure calculations were carried out using the open-source software package ABINIT^2], which is based on DFT. The energy band gap, density of states of Al-doped ZnO were investigated using PAW pseudopotential method within the LDA+U. The calculated density of states was then used in combination with the Boltzmann transport equation^3] to calculate the thermoelectric parameters of Al-doped ZnO. The electronic band structures showed that the position of the Fermi level of the doped sample was shifted upwards in comparison to the undoped one. After doping Al in ZnO, the energy band gap was decreased, Seebeck coefficient and electrical conductivity were increased.Finally, the calculated results were compared with the experimental results. The good agreement of thermoelectric properties between the calculation and the experimental results were obtained.