Band gap estimation from temperature dependent Seebeck measurement-Deviations from the 2e|S|maxTmax relation

In characterizing thermoelectric materials, electrical and thermal transport measurements are often used to estimate electronic band structure properties such as the effective mass and band gap. The Goldsmid-Sharp band gap, E-g = 2e vertical bar S vertical bar T-max(max), is a tool widely employed to estimate the band gap from temperature dependent Seebeck coefficient measurements. However, significant deviations of more than a factor of two are now known to occur. We find that this is when either the majority-to-minority weighted mobility ratio (A) becomes very different from 1.0 or as the band gap (Eg) becomes significantly smaller than 10 k(B)T. For narrow gaps (E-g less than or similar to 6 k(B)T), the Maxwell-Boltzmann statistics applied by Goldsmid-Sharp break down and Fermi-Dirac statistics are required. We generate a chart that can be used to quickly estimate the expected correction to the Goldsmid-Sharp band gap depending on A and S-max; however, additional errors can occur for S < 150 mu V/K due to degenerate behavior. (C) 2015 AIP Publishing LLC.