Grain Size Dependent Comparison of ZnO and ZnGa2O4 Semiconductors by Impedance Spectrometry

We investigated the electrical properties of ZnGa2O4 via AC (alternating current) Impedance Spectroscopy method comparing with ZnO reference material. Experimentally, AC electrical conductivity of ZnO and ZnGa2O4 were found to be a function of temperature and grain size; i.e., the increase in grain size of the ZnO led a decrease in room temperature conductivity from 1.35 × 10−7 S cm−1 to 9.9 × 10−8 S cm−1. The temperature dependent resistivity variation of ZnGa2O4 and ZnO were similar to each other with varied responding temperature. Likewise, the conductivity for ZnGa2O4 decrease from 2.2 × 10−8 S cm−1 to 3.8 × 10−9 S cm−1 upon an increase in grain size from ∼0.5 μm to 100 μm, accordingly. In addition, a rise in temperature caused an increase in conductivity and led to a corresponding shift in the relaxation time towards the lower values. The semicircles in Nyquist plots disappeared at temperature above 250 °C and 700 °C for ZnO and ZnGa2O4, respectively. The AC measurements were also correlated with the size dependent activation energies (171 meV for 0.5 μm ZnO and 1200 meV for 0.5 μm ZnGa2O4).