The use of rare earth ions (REIs)—typically embedded as atomic defects in solids—has emerged as a promising strategy for practical quantum memories. In particular, the Er ion has garnered significant attention due to its telecom C-band optical transition, which makes it a suitable candidate for integration into existing optical fiber networks without the need for photon wavelength conversion. However, successful scalability of such a quantum memory platform would benefit greatly from employing a host material that is fully compatible with silicon and modern CMOS fabrication processes. In this study, we present the synthesis of Er-doped TiO2 thin films directly on standard silicon or silicon-on-insulator (SOI) substrates using atomic layer deposition (ALD). Our thin film exhibits favorable emitter properties at cryogenic temperatures (T = 3.5 K), including a narrow inhomogeneous linewidth and optical lifetime approaching that of bulk values. Additionally, the ALD process provides ample opportunities for device fabrication and integration with other components, further enhancing its potential for practical applications. Overall, our findings suggest that Er-doped TiO2 thin films synthesized via ALD represent a promising approach for developing practical quantum memories that can be seamlessly integrated with silicon photonics. This work lays a foundation for the development of quantum technologies with potential applications in communication, computing, and cryptography.
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