Thermoelectric properties and electronic structure of Al-doped ZnO

Impure ZnO materials are of great interest for high temperature thermoelectric application. In this work, we present the effects of Al-doping on the thermoelectric properties and electronic structures of a ZnO system. We find that, with increasing Al concentrations, the electrical conductivity increases and the thermal conductivity decreases significantly, whereas, the Seebeck coefficient decreases slightly. Nevertheless, the figure of merit (ZT) increases owing to high electrical conductivity and low thermal conductivity. On the other hand, the electronic band structures show that the position of the Fermi level is moved upwards and the bands split near the valence-band top and conduction-band bottom. This is due to the interaction between the Al3p and Zn4s orbitals, which drive the system towards semimetal. Besides, the Density Of States (DOS) analysis shows that the introduction of Al atom obviously reduces the slope d(DOS)/dE near the Fermi level. Based on the calculated band structures, we are able to explain qualitatively the measured transport properties of the Al-doped ZnO system.