Effect of secondary phases on the thermoelectric properties of Zn2GeO4 nano-crystals grown by thermal evaporation on Au coated Si substrate

This study reported the growth of Zn2GeO4 nano-crystals on Au coated Si substrate by thermal evaporation technique using vacuum tube furnace for thermoelectric power generation applications. The thermoelectric properties of nano-crystals were improved by generating the secondary phases in the grown samples using the post-growth annealing at various temperatures (600-900 degrees C). The low energy carriers filtered out at the interface of secondary phases and caused an enhancement in Seebeck coefficient and power factor. The emergence of secondary phases with annealing temperature was confirmed by various characterization techniques. XRD data suggested that samples annealed at 800 and 900 degrees C consisted of three extra secondary phases along with the phases related to Zn2GeO4, ZnO, Si and Au. Raman spectroscopy data demonstrated the presence of strong peak due to Si substrate for all samples but two weak peaks appeared at 375 and 800 cm(-1) for samples annealed at 800 and 900 degrees C. The SEM images shows the presence of randomly oriented nano structures as annealing temperature increase up to 900 degrees C. The Hall measurements were also performed to strengthened our argument.