Thermal characterization of Bi2Te3/Sb2Te3 superlattices

Abstract

Superlattices offer the potential to enhance the figure of merit for thermoelectric cooling by increasing the Seebeck coefficient while decreasing the thermal conductivity compared to bulk samples. The large bulk value of ZT makes superlattices containing ${\mathrm{Bi}}_{\mathrm{2}}{\mathrm{Te}}_{\mathrm{3}}$ attractive for demonstrating benefits of using low-dimensional materials in thermoelectric applications. The present work describes measurements of the effective thermal conductivity normal to ${\mathrm{Bi}}_{\mathrm{2}}{\mathrm{Te}}_{\mathrm{3}}{\mathrm{/Sb}}_{\mathrm{2}}{\mathrm{Te}}_{\mathrm{3}}$ superlattices deposited on GaAs using noncontact pulsed laser heating and thermoreflectance thermometry. The data show a strong reduction in the effective thermal conductivity of the ${\mathrm{Bi}}_{\mathrm{2}}{\mathrm{Te}}_{\mathrm{3}}{\mathrm{/Sb}}_{\mathrm{2}}{\mathrm{Te}}_{\mathrm{3}}$ superlattices compared to bulk ${\mathrm{Bi}}_{\mathrm{2}}{\mathrm{Te}}_{\mathrm{3}},$ which can further increase thermoelectric figure of merit. The dependence of thermal conductivity on superlattice period is found to be weak, particularly at periods above 60 Å. This indicates that disorder in ${\mathrm{Bi}}_{\mathrm{2}}{\mathrm{Te}}_{\mathrm{3}}{\mathrm{/Sb}}_{\mathrm{2}}{\mathrm{Te}}_{\mathrm{3}}$ superlattices may limit the heat conduction process at shorter periods than in Si/Ge superlattices, for which measurements were previously reported in the literature.