Charge build-up and re-distribution in SrTixNb1-xO3 quantum wells and TiO2-SrTiO3 heterostructure

This work examined charge build-up and re-distribution in SrTixNb1-xO3 quantum wells and TiO2-SrTiO3 heterostructure based on thermoelectric power data reported in the literature. In this work, we first identified the equations that best related charge density to the thermoelectric power. Using such equations together with a distributed model that accounted for the layered structure, we computed the charge densities in the two structures over a broad temperature range. Our findings suggested that charge migration from the quantum wells into the substrate was primarily governed by the barrier height at the interface. A very different charge density profile was observed in the heterostructure and the computed charge spread into the substrate was immense (of the order of hundreds of micrometres). By comparing such charge spread with values taken from samples when the TiO2 top layer had been removed, we arrived at the conclusion that it could not have originated from the interface and must have arisen from other sources such as oxygen vacancies (acting as donors) embedded during film deposition.