The effect of a graded In profile on the figure of merit of PbTe

摘要

The present study was aimed at demsonstrating the possibility of producing a graded charge carrier concentration in a PbTe crystal by taking advantage of the concentration profile that is set up by the diffusion of In from an external source. Doping by indium generates deep impurity levels lying close to the edge of the conduction band. The Fermi level pinning effect and the electron population of the In impurity levels, which reduces the minority carrier concentration at elevated temperature, significantly improve the thermoelectric beahvior of the resulting materials. The penetration profiles of In, orignating from an external gaseous or liquid source, were determined using Seebeck coefficient measurements in p-and n-type PbTe crystals. In the p-type crystal, the Seebeck coefficient changed sign as the In concentration induced a change from p-type to n-type character. The thermovoltage of a PbTe crystal in which an In concentration profile, generated by In diffusing from a gaseous source had been established, was determined in the 50 to 530 deg C temperature range. The constant Seebeck coefficient that was observed over the whole temperature range provides the experimental support for the underlying premises of this study.