Abstract
p and n-type bismuth telluride based materials prealloyed by bulk mechanical alloying are directly hot pressed with one-step to yield thermoelectric pn junction. Variation of constitutional element concentrations across the pn interface is characterized by EPMA to determine the interface thickness of pn junction. Electrical resistivity of the interface layer is greater than that of both p and n semiconductor materials. Analytic expressions for Seebeck coefficient and figure of merit versus interface layer size are deduced. Seebeck coefficient of the pn junction is inversely proportional to the ratio of interface layer length to pn junction height (hi/h). It agrees well with experimental result. As for a pn junction with a certain thickness of interface layer, there is a maximum figure of merit at the optimal hi/h; and with a decrease of the thickness of the interface, the maximum increases, correspondingly the optimal hi/h decreases. In other words, pn composite billet with a thinner interface layer can attain larger figure of merit at the same hi/h than the one with a thicker interface. Adjusting process parameter, with proper cutting, thermoelectric properties can be improved greatly, this method for pn junction is feasible.
