Chemically vapor deposited Eu3+:Y2O3 thin films as a material platform for quantum technologies
N. Harada, Alban Ferrier, Diana Serrano, Mauro Persechino, Emrick Briand, Romain Bachelet, Ian C. Vickridge, Jean‐Jacques Ganem, Philippe Goldner, Alexandre Tallaire
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.
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 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.
Abstract Thin films provide nanoscale confinement together with compatibility with photonic and microwave architectures, making them ideal candidates for chip‐scale quantum devices. In this work, we propose a thin film fabrication approach yielding the epitaxial growth of Eu 3+ doped Y 2 O 3 on silicon. We combine two of the most prominent thin film deposition techniques: chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). We report sub‐megahertz optical homogeneous linewidths up to 8 K for the Eu 3+ dopants in the film, and lowest value of 270 kHz. This result constitutes a ten‐fold improvement with respect to previous reports on the same material, opening promising perspectives for the development of scalable and compact quantum devices containing rare‐earth ions.
The development of quantum technologies is generating great interest, as they promise major breakthroughs in computational power, measurement sensitivity and precision, as well as communication security, with potential applications acrossdiverse fields such as healthcare or electronics. In this context, rare-earth-doped oxide thin films represent a competitivesolid-state quantum platform for light–matter interactions. This is due to the ability of rare-earth ions to exhibit quantumcoherent states with long coherence times, combined with the nanometric thickness of the films, which makes them compatible with diverse photonic architectures. Chemical vapor deposition (CVD) offers a fast and cost-effective techniquefor producing thin films with good crystalline quality. However, compared to bulk crystals and ceramics, their propertiesare often degraded, likely due to surface proximity, a higher density of point defects, and strain. The use of epitaxial thinfilms, with a reduced defect density, is expected to lead to improved coherence times. The aim of this PhD project istherefore to obtain epitaxial CVD thin films and to enhance their crystalline properties in order to achieve light–matterinterfaces with long coherence times. Thin films were grown on various substrates, including silicon, oxides (quartz, sapphire, yttria-stabilized zirconia, YSZ), and hybrid substrates with a first layer deposited by molecular beam epitaxy (MBE).In parallel, the influence of post-deposition annealing treatments on the crystalline and optical properties of the films wasinvestigated. Epitaxy on hybrid substrates and YSZ was confirmed, with optical coherence times (T2) of 1.1 µs and 0.8µs, respectively, more than twenty times longer than those measured in polycrystalline films of equivalent composition.This epitaxial architecture paves the way for nanostructuring and integration into photonic devices such as resonators andwaveguides.
Rare-earth ions (REIs) have incomplete 4f shells and possess narrow optical intra-4f transitions due to shielding from electrons in the 5s and 5p orbitals, making them good candidates for solid-state optical quantum memory. The emission of Er3+ in the telecom C-band (1530 nm–1565 nm) makes it especially attractive for this application. In order to build practical, scalable devices, the REI needs to be embedded in a non-interacting host material, preferably one that can be integrated with silicon. In this paper, we show that Er3+ can be isovalently incorporated into epitaxial Y2O3 thin films on Si (111). We report on the synthesis of epitaxial, single-crystalline Er:Y2O3 on Si with a narrow inhomogeneous linewidth in the photoluminescence (PL) spectra, 5.1 GHz (<100 mK), and an optical excited state lifetime of 8.1 ms. The choice of Y2O3 was driven by its low nuclear spin and small lattice mismatch with Si. Using PL and electron paramagnetic resonance, we show that Er3+ substitutes for Y in the crystal lattice. The role of interfacial SiOx, diffusion of silicon into the film, and the effect of buffer layers on the inhomogeneous PL linewidth are examined. We also find that the linewidth decreased monotonically with film thickness but surprisingly exhibits no correlation with the film crystalline quality, as measured by the x-ray rocking curve scans, suggesting other factors at play that limit the inhomogeneous broadening in Y2O3 films.
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.