Engineering Electronic Properties of Thermoelectric Semiconductors

<b>Engineering Electronic Properties of Thermoelectric Semiconductors </b><br/> <br/><b><u>G. Jeffrey SNYDER</u></b><br/> <br/><i>Department of Materials Science and Engineering, Northwestern University</i><br/><i>[email protected]</i><br/><i>thermoelectrics.matsci.northwestern.edu</i><br/> <br/>Thermoelectric semiconductors often have complex electronic properties yet they can be modeled with a simple effective mass model. Good thermoelectric materials require a high weighted mobility [1] which serves as the electronic component to the thermoelectric quality factor [2] that determines peak <i>zT</i>. Often complex band structures with multi-valley Fermi surfaces are associated with high weighted mobility. This complexity arises from orbital chemistry as well as structure. Band convergence combined with the physics of avoided crossings can also be used to explain the band structures and provide strategies for band engineering Half Heusler materials [6].<br/>Many thermoelectric materials such as Bi2Te3 are topological insulators (TI). The correlation can be understood in that the band inversion that causes TI can lead to band warping that leads to high valley degeneracy and low transport mass. [4]<br/>In some systems the Fermi surface pockets can be anisotropic and even non-ellipsoidal, such as the tubes of Fermi surface found in SrTiO3 and Pb and Ge Chalcogenides [5]. Tubes or sheets of Fermi surface rather than ellipsoidal pockets leads to a density of states like 1D or 2D low dimensional materials. By engineering the orbital chemistry complex behavior and unusual properties can be devised even in 3D materials.<br/> <br/>[1] Snyder et. al. <i>Advanced Materials,</i> 32, 2001537 (2020)<br/>[2] X. Y. Zhang et al., <i>Science Advances</i> 6, (2020)<br/>[3] Snyder et. al. <i>Advanced Functional Materials,</i> 202112772 (2022)<br/>[4] Toriyama et al. <i>Cell Reports Physical Science</i> 4, 101392 (2023)<br/>[5] M. K. Brod et al, <i>Journal of Materials Chemistry A, </i>9, 12119, (2021)<br/>[6] M. K. Brod et al, <i>MRS Bulletin</i> 47, 573–583 (2022)