CN center: A more robust silicon defect
Our team identified a promising alternative to the T center: the CN center, which consists of carbon (C) and nitrogen (N) atoms (see Fig. 2, right). The CN center is chemically similar to the T center because N has the same number of protons and electrons as C+H. Like H, N also has non-zero nuclear spin. Because the CN center does not contain H, it will be more robust and easier to achieve in actual devices.
We used advanced first-principles computer simulations to model the defect at the atomic level. These simulations allow us to predict material properties of new systems that have not yet been realized experimentally, and they help guide future efforts to engineer and fabricate novel devices. Specifically, we used density functional theory with state-of-the-art hybrid functionals to accurately predict the stable atomic structures and the corresponding electronic structures of the defects.
We modeled the system by putting up to 1,000 silicon atoms into a simulation box called a “supercell,” and placed the defect atoms accordingly. It turns out, the CN center is stable against decomposition into C and N substitutional and interstitial defects. We also showed that the CN center reproduces the key electronic and optical properties that render the T center attractive for quantum applications. Like the T center, the electronic excited state corresponding to the ZPL transition involves a bound exciton whose spatial range spans beyond the simulation cell sizes that are computationally tractable. To handle this challenge, we developed a new method to extrapolate the excitonic properties from calculations performed in computationally tractable cells, which allows us to reliably calculate the optical properties. We predict a ZPL of 828 meV (1498 nm) within the telecom S-band.
Identifying a hydrogen-free, telecom-wavelength quantum-light emitter in silicon is an important step to bridge the gap between quantum science and scalable technology. The CN center could serve as a practical new building block for quantum devices to potentially accelerate the development of advanced quantum technologies while using the same silicon material that powers today’s electronics.
Funding for this research was provided by the Department of Energy Office of Science, Office of Basic Energy Sciences, through the Co-design Center for Quantum Advantage (C2QA).
FURTHER READING
J. K. Nangoi, M. E. Turiansky, and C. G. Van de Walle, Phys. Rev. B, 113, L060101 (Feb. 10, 2026); https://doi.org/10.1103/zy5b-fskh.