Osaka, Japan – Many next-generation quantum devices rely on single-photon emitters based on optically active defects in solids, known as color centers. Understanding their properties is fundamental to developing novel quantum technologies.
Now, in a study published in APL Materials, a multi-institutional research team led by Osaka University has sought to clarify the origin of the extremely bright color centers at the interface between silicon dioxide (SiO2) and silicon carbide (SiC).
Previous research has demonstrated a range of factors that can play a role in the formation of these interface color centers, including the effect of annealing after oxidation. However, the energy level structure (i.e., the electronic transitions taking place) responsible for luminescence, a crucial factor for understanding the origin of color centers, was completely unknown.
"The origin of color centers at the SiO2/SiC interface has posed a long-standing research problem, and its discovery could boost the development of scalable quantum technologies," explains Kentaro Onishi, lead author of the study.
In this study, the researchers were able to determine the energy levels of color centers at the SiO2/SiC interface. These particular color centers are formed by oxidizing the SiC substrate. Energy levels are formed in the forbidden energy gap of a semiconductor by defects that trap electrons, known as electron traps.
The oxidation conditions during fabrication, including temperature and partial pressure, were thought to influence the densities of color centers and electron traps at the interface, but this work presents the first detailed investigation of the effect of these conditions over a wide range.
The researchers observed a clear correlation between the luminescence of color centers and the density of electron traps, discovering their common origin. The color centers were associated with a specific energy level (i.e., 0.65–0.92 eV from the conduction band edge of SiC), and after comparing the experimental results with theoretical studies, the researchers suggest a specific carbon-related defect as the most promising candidate of the color centers.
"Our results are exciting because we are finally beginning to understand how these interface color centers come to be and how their luminescence works," says Takuma Kobayashi, senior author of the study. "As we deepen our understanding, our hope grows for the realization of quantum technologies using interface color centers. Since these color centers are at the heart of metal-oxide-semiconductor devices, the high compatibility with evolving large-scale integration technologies should pave the way for scalable quantum applications."
As quantum technology relies on the precise control of color centers, this research represents a step toward being able to fabricate such quantum devices in the future.
