Researchers from Korea, led by Prof. Bongjin Simon Mun from Gwangju Institute of Science and Technology, have used ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and low energy electron diffraction (LEED) to investigate how fabrication conditions (annealing in an oxygen-rich environment and an oxygen deficit, low-pressure environment) for a particular perovskite material, SrTiO3, affects its undoped surface and the resulting interfacial layer of the heterostructure.
Certain perovskites can be promising alternatives to silicon-based components for next generation electronic applications. Their structure makes them ideal for use as a base for growing oxide films to form heterostructures with unique electrical properties. The properties of these heterostructures depend on the charge transfer in the interfacial layer between the perovskite substrate and oxide overlayer. This charge transfer can be manipulated via either doping or through the fabrication process.
By using an undoped surface, the researchers wanted to examine the changes that occur on the surface of the substrate without interference from the dopants. "The presence of doping can interfere with correct interpretation of the surface defect states, which can be critical to apprehend the electrical properties of heterostructures. Our study on undoped SrTiO3 provides unbiased characteristics of SrTiO3 substrate," says Prof. Mun.
In the oxygen environment, an electron depletion layer formed as the Sr atoms in the substrate migrated to the surface of the film to react with oxygen and form a stable oxide layer. In the low-pressure oxygen deficit environment, the formation of such a depletion layer was limited as the oxide layer was formed due to the reduction of the TiO2 layer that generated electrons.
In both environments, a similar oxide layer was formed, but the electronic properties of the structure differed as the electron depletion layer is key to the conductivity of the structure.
"Our work shows clearly how the electrical properties of devices can be tuned by adjusting the population of electrons near the surface region, which is a very fundamental and important result indicating that future electronic devices can be realized with material characterization at the atomic level," says Prof. Mun. "In the long run, our study on SrTiO3 will lay out a solid foundation for advanced electronic devices that will enable a better lifestyle for us."