GIST Develops Atomic-Level Next-Generation Electronic Device Characteristic Control Method

(From the bottom left, counterclockwise) Professor Moon Bong-jin, student Lim Ho-jun, student Seo Min-sik, student Kang Ha-bin, student Jung Moon-jung Photo by Gwangju Institute of Science and Technology.

[Asia Economy Honam Reporting Headquarters Reporter Cho Hyung-joo] GIST announced on the 21st that Professor Moon Bong-jin’s research team from the Department of Physics and Optical Science succeeded in real-time observation of electronic, chemical, and structural state changes of heterojunction complex oxide substrates.

The research team discovered chemical composition changes and the formation of space charge layers, along with the resulting bending of energy bands on the surface of strontium titanate substrates exposed to a high-temperature oxygen environment, using an ambient pressure photoelectron spectroscopy system based on a synchrotron radiation accelerator.

Heterojunction complex oxides are materials made by stacking oxides with different properties layer by layer, where the constituent materials interact through interfaces to realize excellent electrical, magnetic, thermal, and mechanical functionalities.

Key phenomena in next-generation electronic device development, such as giant magnetoresistance, metal-insulator transitions, high-temperature superconductors, and two-dimensional electron gases, are all characteristics realized within heterojunction complex oxide structures. However, the principles behind the manifestation of these functionalities and their operating mechanisms have not yet been clearly elucidated.

Since changes in the chemical, electrical, and structural properties of substrate surfaces under the temperature and pressure conditions used to grow functional oxides significantly influence the performance of the functional oxides grown on them, it is essential to thoroughly understand the surface dynamics of substrates to design optimal growth conditions for performance enhancement.

The research team performed in-situ analysis of the chemical and electronic structure of strontium titanate substrates terminated with an outermost titanium dioxide layer inside an ambient pressure photoelectron spectroscopy chamber.

By controlling the gas environment inside the chamber from ultra-high vacuum to oxygen gas pressure of 0.1 mbar and the temperature environment from room temperature to 600℃, they confirmed in real time the formation of space charge layers due to atomic migration and chemical structural changes on the strontium titanate substrate surface, as well as the role of the oxygen environment.

Professor Moon Bong-jin stated, “In this study, we excluded doping effects that could influence the electronic, chemical, and structural states of the substrate to reveal the pure surface space charge characteristics of strontium titanate substrates,” adding, “Through this research, we significantly enhanced the possibility of controlling the properties of substrates and functional materials and their application as next-generation electronic materials.”

This research was conducted with support from the National Research Foundation of Korea and GIST Research Institute. It was published as a cover paper on June 14 in the prestigious journal of the Royal Society of Chemistry, the Journal of Materials Chemistry C.

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