Electrical, optical, and thermoelectric properties of Ga2O3(ZnO)9

Abstract

The physical properties of the sintered sample of Ga₂O₃(ZnO)₉, a member of the homologous series Ga₂O₃(ZnO)_m and recently found to have new structures, were investigated. The material was found to be a new transparent conducting oxide, and is composed of relatively abundant and inexpensive elements compared to indium. The electrical conductivity of a sintered low 57% density sample, 13 S cm⁻¹ as fired at 1723 K, could be varied by postheating in air or a reducing gas (H₂ 3% : Ar 97%) flow. The changes in conductivity were associated with the variations of absorbance in the visible light range, while the optical band gap, or the absorption edge, was almost unchanged. The thermoelectric properties showed n-type behavior. It was relatively easy to vary the thermoelectric properties through redox treatments, and reversibility was also observed. The maximum figure of merit Z reaches a value of close to 10⁻⁴ K⁻¹ at 660 K for a sample with density of only 73%. The potential of Ga₂O₃(ZnO)₉ as a thermoelectric material appears to be similar to or even greater than the related In₂O₃(ZnO)_m system, and since Ga₂O₃(ZnO)₉ has an advantage in the abundance of constituent elements, it is revealed to be a promising system for further investigations.