Thickness dependent thermoelectric properties of SrTiO$_{3}$/SrLaTiO$_{3}$ and SrZrO$_{3}$/SrLaTiO$_{3}$ heterostructures

Thermoelectric power generators will be required for future sensor network systems. SrTiO$_{3}$ (STO) [1] is one candidate thermoelectric material due to its non-toxicity and comparable power factor to Bismuth telluride. The energy conversion efficiency of SrTiO$_{3}$--based thermoelectric energy conversion elements has been reported to be enhanced by quantum size effects, such as the two dimensional (2D) electron gas in SrTiO$_{3}$/SrTi$_{0.8}$Nb$_{0.2}$O$_{3}$/SrTiO$_{3}$ [2]. Nevertheless, a complete understanding of the mechanisms for the reported increase in efficiency are missing owing to a lack of understanding of the thickness dependence of the transport properties. In the talk, we will present a study of the thickness dependence of the transport properties of SrTiO$_{3}$/SrLaTiO$_{3}$ and SrZrO$_{3}$/SrLaTiO$_{3}$ heterostructures. The SrZrO$_{3}$/SrLaTiO$_{3}$ interface has a large conduction band off-set of 1.9 eV [3] which can be utilized to confine electrons in a 2D quantum well. Characterization of the thermopower, conductivity, and Hall effect will be presented as a function of the SrLaTiO$_{3}$ thickness down to a few unit cells and the implications of the thickness dependence of the transport properties on carrier confinement and increasing the efficiency STO-based 2DEG quantum well structures will be discussed. [1] J. Baniecki et al, Appl. Phys. Lett. 99, 232111 (2011); [2] H. Otha et al., Nature materials, 6, 129 (2007); [3] R Schafranek et al, J. Phys. D: 45 055303 (2012)