Thermoelectric Properties of SrTiO₃: Bulks, Superlattices, and Transistors

Abstract

Here I review the thermoelectric properties of electron doped SrTiO₃. Since density of states effective mass of electron carrier in SrTiO₃ crystal is rather large, heavily electron doped SrTiO₃ crystal exhibits rather large Seebeck coefficient (S). The reliable thermoelectric figure of merit, ZT is ∼0.08 at room temperature and ∼0.3 at 1,000 K, which is highest among metallic oxides. Recently, we found that high-density (∼10²¹ cm^-3) two-dimensional (2D) electron layers in SrTiO₃ crystal exhibits giant S, which is ∼5 times larger than that of simple bulk, when the layer thickness is as thin as one unit cell (0.3905 nm). The 2D electron layer is realized by superlattices of SrTiO₃/SrTi_0.8Nb_0.2O₃ or TiO₂/SrTiO₃ heterointerface. Very recently, we fabricated high performance field effect transistors (FETs) on SrTiO₃ single crystal to modulate the Seebeck coefficient by applying the gate voltage.