Minority carrier barrier heterojunctions for improved thermoelectric efficiency

Abstract

We propose and demonstrate the beneficial use of minority carrier blocking layers to lessen bipolar conduction at elevated temperatures and increase the Seebeck coefficient in a thermoelectric material. Bipolar conduction, caused by thermally activated intrinsic carriers in semiconductors, causes a detrimental “roll-over” in the Seebeck coefficient and increase in thermal conductivity, measured as a function of temperature. We propose that these negative effects can be lessened or delayed in a small band gap host matrix by incorporating wider band gap semiconductor layers to impede the thermal diffusion of minority carriers over majority carriers. To prove this concept, a composite material grown by molecular beam epitaxy of p-type InAs layers and electron blocking p-type AlSb layers were grown and measured. We show improved thermoelectric properties over just p-type InAs in measurements from 110K to 600K.