Defect Chemistry and Dopability of Telluride Diamond-Like Semiconductors and Ordered Vacancy Compounds for Thermoelectric Applications

Computation-driven search for candidate thermoelectric materials has recently resulted in several successes, but many of the predicted materials often prove to be difficult to dope in the lab. This presentation will review our recent computational and experimental efforts to tailor and understand defect chemistry and dopabaility of a chemically-diverse set of telluride-based diamond-like semiconductors (DLS) of interest for their potential as thermoelectrics. We consider the I_BIIITe₂ with I_B=(Cu,Ag), III=(In,Ga) and Cu₂(Zn,Cd,Hg)(Si,Ge,Sn)Te₄ material space, and use first-principles methods and experimental phase boundary mapping to comprehensively assess dopabilities in this search space. These materials are typically observed to be p-type, but a materials descriptor suggests that they would be more effective as thermoelectrics if they could be doped n-type. Therefore, we comprehensively establish the achievable range of carrier concentrations using calculations of phase stability, defect formation energies, and carrier concentrations. Using phase boundary mapping, experimental carrier concentrations are measured and compared to the predicted values, showing a correspondance within a few orders of magnitude. For all compounds, a delicate competition between I_III, III_I, and V_I defects governs the achievable range of carrier concentrations -- and enhancing n-type behavior requires suppressing the I_III and V_I defects while enhancing the III_I antisites. Using this observation as a design strategy, we identify candidate diamond like semiconductors that may be more amenable to n-type doping. The results of this comprehensive search are used to generate a chemically intuitive framework for predicting dopabilities in this family of materials without the need to carry out full-scale first-principles analysis.