on silicon*

Erbium-doped cerium oxide (Er:CeO₂) is a promising defect-host combination for applications in quantum memories for wide-area fiber optic-based quantum networks, due to the telecom-compatible (~1.5 μm) 4f-4f optical transition of Er, predicted long electron spin coherence time for defects in CeO₂,¹ and small lattice mismatch between silicon and CeO₂. Here we report on epitaxial Er:CeO₂ thin films grown on silicon by molecular beam epitaxy, with Er doping in the 1-100 ppm regime.² We verify the CeO₂ host structure via thorough microstructural study, and then characterize the spin and optical properties of the embedded Er³⁺ ions as a function of doping density. Studying the Z₁-Y₁ optical transition near 1530 nm at 3.5 K with 2-3 ppm Er, we find spectral diffusion-limited homogeneous linewidths as narrow as 5 MHz, along with inhomogeneous linewidths of 10 GHz and optical excited state lifetimes of 3.5 ms; further measurements at 4 K yield EPR linewidths of 250 MHz. We then discuss routes for optical and spin linewidth improvement via growth optimization and post-growth treatment.

(1) S. Kanai, et al. PNAS. 119, e2121808119 (2022).

(2) G. Grant, et al. arXiv:2309.16644 (2023).