Optimizing the thermoelectric properties of thermally evaporated AgSnO2 thin films by post growth annealing process

In this manuscript, we have studied the thermoelectric properties of Silver Tin Oxide thin films deposited by thermal evaporation method. Tube furnace was used to deposit thin films on silicon (100) substrate by evaporating a mixture of Silver (Ag) and Tin (Sn) having (1:1) ratio. The experimental conditions were set as: distance from source to substrate (5 cm), Evaporation temperature inside the tube furnace (1000 degrees C), flow rate of oxygen gas (120sccm) and evaporation time for deposition was set as 40 min. Furthermore, diffusion of oxygen and mobility of charge carriers was controlled by annealing the samples at various temperatures after successful growth. We have observed that the value of Seebeck coefficient was increased from 242 to 630 mu V/oC by increasing the annealing temperature from 600 to 900 degrees C. This behavior is due the fact that increasing annealing temperature causes the mobility of charge carriers increased due to which simultaneous enhancement in Seebeck coefficient and electrical conductivity is observed. The enhancement in the carrier mobility was demonstrated by the fact that extra oxygen atoms resulted in the generation of grain boundaries defects which block the slow moving carriers and only fast moving electrons are able to reach cold end of sample. XRD and Raman spectroscopy results confirmed the hexagonal structure of AgSnO2. XRD data further confirmed the degradation of crystal quality due to increase in annealing temperature. The morphology of as grown and annealed samples was observed with the help of SEM.