Harnessing Atomic Layer Deposition and Diffusion to Spatially Localize Rare-Earth Ion Emitters
Alban Ferrier, N. Harada, Marion Scarafagio, Emrick Briand, Jean‐Jacques Ganem, Ian C. Vickridge, Antoine Seyeux, Philippe Marcus, Diana Serrano, Philippe Goldner, Alexandre Tallaire
The control of rare-earth ion doping profiles is a key challenge for several photonic applications and quantum technologies that require spatially localized emitters. In this work, we propose to use atomic layer deposition (ALD) followed by an annealing post-treatment to localize europium emitters close to the surface of a Y 2 O 3 film or a Y 2 SiO 5 single crystal by exploiting in-diffusion. Indeed, ALD is a conformal method that can provide in-depth nanometer-scale positioning accuracy on a large scale. However, the post-thermal annealing required to achieve higher crystalline quality and activate diffusion needs to be precisely controlled to maximize our ability to localize ions. In this paper, we evaluate europium ion diffusion in an ALD-grown Eu 2 O 3 /Y 2 O 3 /Si stack using Rutherford backscattering spectroscopy (RBS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). We then extend this approach to investigate diffusion from a Eu 2 O 3 ALD film into a single-crystalline substrate of Y 2 SiO 5 (YSO), a technologically relevant material system for quantum applications. We determine the Eu 3+ diffusion coefficients in both cases and show that diffusion starts at 950 °C in the polycrystalline Y 2 O 3 ALD submicron film, whereas it becomes significant only above 1200 °C in single-crystal YSO. Finally, spectral hole burning of such in-diffused emitters revealed homogeneous lines as narrow as 2 MHz. This study indicates that appropriate annealing of ALD-grown rare-earth oxide films can be harnessed to create localized dopants that preserve their outstanding optical properties, a prerequisite for their integration into photonic and quantum devices.
The control of rare-earth ion doping profiles is a key challenge for several photonic applications and quantum technologies that require spatially localized emitters. In this work, we propose to use atomic layer deposition (ALD) followed by an annealing post-treatment to localize europium emitters close to the surface of a Y 2 O 3 film or a Y 2 SiO 5 single crystal by exploiting in-diffusion. Indeed, ALD is a conformal method that can provide in-depth nanometer-scale positioning accuracy on a large scale. However, the post-thermal annealing required to achieve higher crystalline quality and activate diffusion needs to be precisely controlled to maximize our ability to localize ions. In this paper, we evaluate europium ion diffusion in an ALD-grown Eu 2 O 3 /Y 2 O 3 /Si stack using Rutherford backscattering spectroscopy (RBS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). We then extend this approach to investigate diffusion from a Eu 2 O 3 ALD film into a single-crystalline substrate of Y 2 SiO 5 (YSO), a technologically relevant material system for quantum applications. We determine the Eu 3+ diffusion coefficients in both cases and show that diffusion starts at 950 °C in the polycrystalline Y 2 O 3 ALD submicron film, whereas it becomes significant only above 1200 °C in single-crystal YSO. Finally, spectral hole burning of such in-diffused emitters revealed homogeneous lines as narrow as 2 MHz. This study indicates that appropriate annealing of ALD-grown rare-earth oxide films can be harnessed to create localized dopants that preserve their outstanding optical properties, a prerequisite for their integration into photonic and quantum devices.
Atomic layer deposited (ALD) Y 2 O 3 thin films have been thoroughly investigated for optical or electronic applications. The coherent spectroscopy of lanthanide ions doped into this material has also recently attracted increasing interest in the field of quantum technologies for which they are considered promising candidates in quantum memories or as spin–photon interfaces. However, these most demanding applications require a deep control over the local positioning of the ions and their close environment in the crystalline matrix. This study focuses on the structural as well as optical properties of Eu 3+ and Er 3+ dopants in Y 2 O 3 using photoluminescence (PL), luminescence decay times, and inhomogeneous line width (Γ inh ) measurements within this particular context. While as-grown ALD films do not provide an ideal host for the emitters, we demonstrate that by optimizing the deposition conditions and using appropriate annealing post treatments narrow inhomogeneous lines can be obtained for the 7 F 0 ↔ 5 D 0 transition of Eu 3+ even for nanoscale films. Furthermore, about 1.5 ms lifetime has been measured for the infrared telecom transition of Er in ultrathin films (<10 nm), which is an order of magnitude higher than in nanoparticles of the same size. These results validate optimized rare-earth-doped ALD Y 2 O 3 films as a suitable platform for photonics applications where few-nanometer-thick films with well-localized emitters are mandatory. This approach provides the first building blocks toward the development of more complex devices for quantum sensing or hybrid structures coupled with other systems such as two-dimensional materials.
Rare earth ions hosted in solids are good candidates for quantum technologies due to their chemical stability and optical and spin transitions exhibiting long coherence lifetimes. While bulk oxide crystals are usually the preferred host material, the development of a scalable silicon-compatible thin film platform would be desirable. In this paper, we report on the growth of Y2(1−x)Eu2xO3 thin films on silicon in the full range of Eu3+ concentration by direct liquid injection chemical vapor deposition (CVD). Our sub-micrometer polycrystalline films with a strong-(111) texture were grown for all compositions into the bixbyite cubic phase. The variation of growth rates with temperature and flow indicated that deposition occurred through a mass-transport controlled regime. Optical assessment of the Eu-doped thin films showed inhomogeneous linewidths as narrow as 50 GHz and fluorescence lifetimes of 1 ms for the lowest concentrations. Finally, a spectral hole was successfully burned in a 200 nm-thin film with a 2% Eu doping leading to a homogeneous linewidth of 11 MHz. These values are still below those reported for bulk single crystals indicating that additional decoherence mechanisms exist in such nanometric films, which might be alleviated by further improvement of the crystalline quality. Nevertheless, these results pave the way to the use of CVD-grown Eu:Y2O3 thin films as a platform for integrated quantum devices.
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.
Coherent quantum devices play a central role in quantum science and engineering. Rare-earth ions such as erbium in solids feature numerous 4f- intra-shell transitions that are effectively shielded from their crystalline surroundings by closed outer shells, allowing for long spin coherence times and narrow optical transitions. Recent ensemble experiments have established the rare-earth doped crystals as the leading materials for optical quantum memories. However, the development of large-scale quantum devices based on rare-earth doped materials has remained a challenge. Here we describe a scalable quantum photonic platform based on epitaxially grown oxide thin films doped with trivalent ions on silicon substrates. The platform builds upon the recent developments of high quality epitaxial rare-earth doped oxides on silicon, and highlights the integration of quantum coherent materials with existing silicon technologies for ultimate device scalability. The proposed device platform builds upon our capability to epitaxially grow high quality, near-lattice-matched Y2O3 thin films on silicon. The epitaxial thin film is of high structural quality and offers several distinct advantages: (1) significantly less optical loss and better quantum emitter coherence; (2) atomic precision placement of rare-earth emitters (via delta doping) with respect to the photonic mode for controllable ion-photon coupling; (3) scalable top-down device fabrication using standard lithography and etching techniques; (4) heterogeneous integration with silicon takes full advantage of existing silicon photonics technologies for routing, tuning, and modulation of the quantum emission from rare-earth ions.
The obtention of quantum-grade rare-earth-doped oxide thin films that can be integrated with optical cavities and microwave resonators is of great interest for the development of scalable quantum devices. Among the different growth methods, chemical vapor deposition (CVD) offers high flexibility and has demonstrated the ability to produce oxide films hosting rare-earth ions with narrow linewidths. However, growing epitaxial films directly on silicon is challenging by CVD due to a native amorphous oxide layer formation at the interface. In this manuscript, we investigate the CVD growth of erbium-doped yttrium oxide (Er:Y2O3) thin films on different substrates, including silicon, sapphire, quartz, or yttria stabilized zirconia (YSZ). Alternatively, growth was also attempted on an epitaxial Y2O3 template layer on Si (111) prepared by molecular beam epitaxy (MBE) in order to circumvent the issue of the amorphous interlayer. We found that the substrate impacts the film morphology and the crystalline orientations, with different textures observed for the CVD film on the MBE-oxide/Si template (111) and epitaxial growth on YSZ (001). In terms of optical properties, Er3+ ions exhibit visible and IR emission features that are comparable for all samples, indicating a high-quality local crystalline environment regardless of the substrate. Our approach opens interesting prospects to integrate such films into scalable devices for optical quantum technologies.
The obtention of quantum-grade rare-earth doped oxide thin films that can be integrated with optical cavities and microwave resonators is of great interest for the development of scalable quantum devices. Among the different growth methods, Chemical Vapour Deposition (CVD) offers high flexibility and has demonstrated the ability to produce oxide films hosting rare-earth ions with narrow linewidths. However, growing epitaxial films directly on silicon is challenging by CVD due to a native amorphous oxide layer formation at the interface. In this manuscript, we investigate the CVD growth of erbium-doped yttrium oxide (Er:Y2O3) thin films on different substrates, including silicon, sapphire, quartz or yttria stabilized zirconia (YSZ). Alternatively, growth was also attempted on an epitaxial Y2O3 template layer on Si (111) prepared by molecular beam epitaxy (MBE) in order to circumvent the issue of the amorphous interlayer. We found that the substrate impacts the film morphology and the crystalline orientations, with different textures observed for the CVD film on the MBE-oxide/Si template (111) and epitaxial growth on YSZ (001). In terms of optical properties, Er3+ ions exhibit visible and IR emission features that are comparable for all samples, indicating a high-quality local crystalline environment regardless of the substrate. Our approach opens interesting prospects to integrate such films into scalable devices for optical quantum technologies.