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This work describes through semiclassical Boltzmann transport theory andsimulation a novel nanostructured material design that can lead tounprecedentedly high thermoelectric power factors, with improvements of morethan an order of magnitude compared to optimal bulk material power factors. Thedesign is based on a specific grain/grain-boundary (potential well/barrier)engineering such that: i) carrier energy filtering is achieved using potentialbarriers, combined with ii) higher than usual doping operating conditions suchthat high carrier velocities and mean-free-paths are utilized, iii) minimalcarrier energy relaxation after passing over the barriers to propagate the highSeebeck coefficient of the barriers into the potential wells, and importantly,iv) the formation of an intermediate dopant-free (depleted) region. The designconsists thus of a three-region geometry, in which the high doping resides inthe center/core of the potential well, with a dopant-depleted region separatingthe doped region from the potential barriers. It is shown that the filteringbarriers are optimal when they mitigate the reduction in conductivity theyintroduce, and this can be done primarily when they are clean from dopantsduring the process of filtering. The potential wells, on the other hand, areoptimal when they mitigate the reduced Seebeck they introduce by: i) notallowing carrier energy relaxation, and importantly ii) by mitigating thereduction in mobility that the high concentration of dopant impurities cause.Dopant segregation, with clean dopant-depletion regions around the potentialbarriers, serves this key purpose of improved mobility towards thephonon-limited mobility levels in the wells. Using quantum transportsimulations as well as semi-classical Monte Carlo simulations we also verifythe important ingredients and validate this clean-filtering design.

Nanostructured potential well/barrier engineering for realizing unprecedentedly large thermoelectric power factors