Optimization of Seebeck coefficients of strain-symmetrized semiconductor heterostructures

Abstract

A nonmonotonic thermopower (S) as a function of the carrier concentration (ne) has been reported for III–V semiconductor superlattices (SLs), deviating from the Pisarenko relation. However, |S| has been shown to decrease with increasing ne in n-type Si/Ge heterostructures, the widely used systems for numerous applications. Here, we illustrate that S of a SinGem SL, with n Si and m Ge monolayers, can deviate from the Pisarenko relation depending on the period and the composition; for example, oscillations of S of a Si12Ge12 SL reach a peak |S|=540 μV/K at ne=1.3×1020 cm−3, 5.4 times higher than that of bulk Si at the same doping level. Additionally, S shows an interesting sign-change nature at certain carrier concentrations. We demonstrate the direct relationship between the electronic structure and S of strain-symmetrized Si/Ge SLs using two independent modeling approaches. We anticipate that this relationship will provide insight into fully exploiting S as a tool to control electronic properties of Si/Ge heterostructures as well as future technology-enabling materials. Furthermore, we expect that this analysis will encourage future investigations to enhance thermoelectric properties of a broad class of semiconductor SLs in the high-doping regime.