Growth of Zn2GeO4 thin film by thermal evaporation on ITO substrate for thermoelectric power generation applications

Abstract

In this paper, we have reported the growth of Zn2GeO4 thin film and investigated its potential for thermoelectric power generation applications. Zn2GeO4 alloy thin film was grown on Indium coated glass substrate by the evaporation of Zn and Ge metals with constant oxygen gas flow rate of 100 sccm in tube furnace. The grown film was cut into pieces and annealed at various temperatures from 500° to 700°C with a step of 100 °C in a programmable furnace for one hour. The structure of as grown and annealed thin films was verified by XRD and Raman spectroscopy measurements. The XRD data evident that Zn2GeO4 alloy hexagonal structure along with GeO2 and ZnO phases were observed at annealing temperatures 600 and 700 °C but below this temperature no alloy phase was detected by XRD and Raman Spectroscopy. To calculate the thermoelectric properties, temperature dependent Seebeck measurements were performed in the temperature range of 25–100 °C. It was observed that the value of Seebeck coefficient was increased from 91 to 847 μV/K as the annealing temperature increases from 500° to 700°C. This behavior was explained as; high temperature causes stress and cracks in the grown films which may induce electric and thermal discontinues at tips of cracks which cause high thermoelectric concentration. Scanning electron microscope images verified the development of cracks in the samples as annealing temperature increases. The behavior of Seebeck coefficient with the measurement temperature was also observed and explained in detail. The high value of Seebeck coefficient suggested that this material can be a potential candidate for thermoelectric power generation applications in near future.