Compensation of Zn substitution and secondary phase controls effective mass and weighted mobility in In and Ga co-doped ZnO material
Oanh Kieu Truong Le, Anh Tuấn Thanh Phạm, Ngoc Kim Pham, Trang Huyen Cao Pham, Trương Hữu Nguyễn, Dung Van Hoang, Hanh Kieu Thi Ta, Dai Cao Truong, Hoa Thi Lai, Ung Thi Dieu Thuy, Vinh Cao Trần, Thắng Bách Phan
Abstract
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 μw and quality factor B is discussed in ZnO system. The results show that the secondary spinel phase Ga2O3(ZnO)9 not only impacts on κ but also on σ and S at 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 μw reduction, and a large B enhancement. As a result, In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PF improvement by 112.8%, owing to enhanced Seebeck coefficient by 110% as compared to the good Zn-substitution sample.