  Cross-plane superlattices composed of nanoscale layers of alternating
potential wells and barriers have attracted great attention for their potential
to provide thermoelectric power factor improvements and higher ZT figure of
merit. Previous theoretical works have shown that the presence of optimized
potential barriers could provide improvements to the Seebeck coefficient
through carrier energy filtering, which improves the power factor by up to 40%.
However, experimental corroboration of this prediction has been extremely
scant. In this work, we employ quantum mechanical electronic transport
simulations to outline the detrimental effects of random variation,
imperfections and nonoptimal barrier shapes in a superlattice geometry on these
predicted power factor improvements. Thus we aim to assess either the
robustness or the fragility of these theoretical gains in the face of the types
of variation one would find in real material systems. We show that these power
factor improvements are relatively robust against: overly thick barriers,
diffusion of barriers into the body of the wells, and random fluctuations in
barrier spacing and width. However, notably, we discover that extremely thin
barriers and random fluctuation in barrier heights by as little as 10% is
sufficient to entirely destroy any power factor benefits of the optimized
geometry. Our results could provide performance optimization routes for
nanostructured thermoelectrics and elucidate the reasons why significant power
factor improvements are not commonly realized in superlattices, despite
theoretical predictions.
