Thermoelectric properties of Zn2GeO4 nano-crystals grown on ITO and Au coated Si substrates by thermal evaporation

Abstract

We have reported the comparison of thermoelectric properties of Zn2GeO4 samples grown on ITO and Au coated Si substrates. Mixed powder of Zn and Ge with 1:1 ratio was evaporated in the tube furnace on ITO and Si substrates using identical experimental conditions. After growth, as grown samples were annealed at different temperatures in oxygen environment. Seebeck and Hall data suggested that the sample grown on Au coated Si substrate (Au/Si) has higher values of electromotive force, electrical conductivity and power factor as compared to sample grown on ITO substrate, because the sample grown on Au/Si substrate has high density of secondary phases. The presence of secondary phases resulted in the enhancement of Seebeck coefficient and mobility of charge carriers. It is also observed that thermoelectric properties of Zn2GeO4 samples were also improved due to increased of annealing temperature due the emergence of cracks and secondary phases in the annealed samples. This argument was further supported by various characterizations tools. XRD data confirmed the formation of Zn2GeO4 crystal along with the generation of new phases as the annealing temperature increased up to 900 °C. Furthermore, XRD data demonstrated that the sample grown on Au/Si has prominent Zn2GeO4 phases but the sample grown on ITO substrate has weak Zn2GeO4 peak along with ZnO phases. SEM images demonstrated the generation of cracks on the surface of Zn2GeO4 with annealing temperature due to thermal stress. Raman spectroscopy measurements also supported the XRD and SEM results.