Effect of quantum-well structures on the thermoelectric figure of merit

Currently the materials with the highest thermoelectric figure of merit Z are ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ alloys. Therefore these compounds are the best thermoelectric refrigeration elements. However, since the 1960s only slow progress has been made in enhancing Z, either in ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ alloys or in other thermoelectric materials. So far, the materials used in applications have all been in bulk form. In this paper, it is proposed that it may be possible to increase Z of certain materials by preparing them in quantum-well superlattice structures. Calculations have been done to investigate the potential for such an approach, and also to evaluate the effect of anisotropy on the figure of merit. The calculations show that layering has the potential to increase significantly the figure of merit of a highly anisotropic material such as ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$, provided that the superlattice multilayers are made in a particular orientation. This result opens the possibility of using quantum-well superlattice structures to enhance the performance of thermoelectric coolers.