Thermopower enhancement and optimal ZT in p-n junction arrays

Thermoelectric effects in different types of p-n junction systems are considered theoretically, and the thermoelectric power S is calculated in a rigorous approximation. S for a single p-n junction is found to be rather large, due to the thermal factor E/sub g//kT (E/sub g/ being the band gap). This factor naturally appears in the expression for S for an asymmetric junction, and cancels from S for a symmetric junction. The thermopower of individual p-n junctions (S/sub n/) add for an array of in-series junctions (-p-n-p-n-p-...), and this result may be used for the enhancement of the Seebeck coefficient in opal-type 3-D superlattices. The figure of merit ZT of the p-n junction system is shown to have an upper bound of 1.