Compensation of Zn substitution and secondary phase controls effective mass and weighted mobility in In and Ga co-doped ZnO material

Conductivity σ and thermal conductivity κ are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration. Therefore, improving thermoelectric (TE) performance is challenging. Here, the first-time analysis of secondary phase-controlled TE performance in terms of density-of-state effective mass md∗, weighted mobility μwand quality factor Bis discussed in ZnO system. The results show that the secondary spinel phase Ga2O3(ZnO)9not only impacts on κbut also on σand Sat high temperature, while the effect of carrier concentration seem to be dominant at low temperature. For the high-spinel-segregation sample, a compensation of dopant atoms from the spinel to substitutional sites in the ZnO matrix at high temperature leads to a low decreased rate of temperature-dependent md∗. The compensation process also induces a band sharpening, a small μwreduction, and a large Benhancement. As a result, In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PFimprovement by 112.8%, owing to enhanced Seebeck coefficient by 110% as compared to the good Zn-substitution sample.