Journal of Vacuum Science & Technology A Vacuum Surfaces and Films
Microstructural and optical characterization of Erbium-doped calcium tungstate films on yttria-stabilized zirconia
Sagar Kumar Seth, Bonnie Y.X. Lin, Ignas Masiulionis, Gregory D. Grant, Claire M. McDermott, F. Joseph Heremans, Jiefei Zhang, James M. LeBeau, D. D. Awschalom, Supratik Guha
Er3+-doped bulk CaWO4 has been demonstrated to be a promising platform for quantum repeaters. However, the use of bulk crystals presents challenges for device integration and scalability. In this paper, we address the scalability of this platform by realizing thin-film CaWO4 growth on yttria-stabilized zirconia wafers, a step toward a CMOS-compatible heterogeneous platform. The films were deposited via radio-frequency magnetron sputtering, a scalable method, followed by postdeposition annealing and were in situ doped with Er. Optical characterization of the Er3+ ions in these films reveals lifetimes of 2.28 ± 0.16 ms, inhomogeneous linewidths of 48.29 ± 0.96 GHz, and a spectral-diffusion-limited homogeneous linewidth of 12.61 ± 2.79 MHz. These results are comparable to previously reported Er3+ in rare-earth oxide thin film hosts. The results highlight the potential of sputtered Er3+-doped CaWO4 thin films for quantum coherent applications.
Er3+-doped bulk CaWO4 has been demonstrated to be a promising platform for quantum repeaters. However, the use of bulk crystals presents challenges for device integration and scalability. In this paper, we address the scalability of this platform by realizing thin-film CaWO4 growth on yttria-stabilized zirconia wafers, a step toward a CMOS-compatible heterogeneous platform. The films were deposited via radio-frequency magnetron sputtering, a scalable method, followed by postdeposition annealing and were in situ doped with Er. Optical characterization of the Er3+ ions in these films reveals lifetimes of 2.28 ± 0.16 ms, inhomogeneous linewidths of 48.29 ± 0.96 GHz, and a spectral-diffusion-limited homogeneous linewidth of 12.61 ± 2.79 MHz. These results are comparable to previously reported Er3+ in rare-earth oxide thin film hosts. The results highlight the potential of sputtered Er3+-doped CaWO4 thin films for quantum coherent applications.
This work explores erbium-doped calcium molybdate (Er:CaMoO4) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the ∼1.5 μm Er3+ 4f–4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction, and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO4 formation that can be in situ doped with Er (typically 2–100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology, while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO4 films. We perform preliminary optical and microwave characterization on the suspected Y1–Z1 transition of 2 ppm, 200 nm epitaxial Er:CaMoO4 annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.
This work explores erbium-doped calcium molybdate (Er:CaMoO4) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the ∼1.5 μm Er3+ 4f–4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction, and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO4 formation that can be in situ doped with Er (typically 2–100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology, while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO4 films. We perform preliminary optical and microwave characterization on the suspected Y1–Z1 transition of 2 ppm, 200 nm epitaxial Er:CaMoO4 annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.
Rare-earth ion dopants in solid-state hosts are ideal candidates for quantum communication technologies, such as quantum memories, due to the intrinsic spin–photon interface of the rare-earth ion combined with the integration methods available in the solid state. Erbium-doped cerium oxide (Er:CeO2) is a particularly promising host material platform for such a quantum memory, as it combines the telecom-wavelength (∼1.5μm) 4f–4f transition of erbium, a predicted long electron spin coherence time when embedded in CeO2, and a small lattice mismatch with silicon. In this work, we report on the epitaxial growth of Er:CeO2 thin films on silicon using molecular beam epitaxy, with controlled erbium concentration between 2 and 130 parts per million (ppm). We carry out a detailed microstructural study to verify the CeO2 host structure and characterize the spin and optical properties of the embedded Er3+ ions as a function of doping density. In as-grown Er:CeO2 in the 2–3 ppm regime, we identify an EPR linewidth of 245(1) MHz, an optical inhomogeneous linewidth of 9.5(2) GHz, an optical excited state lifetime of 3.5(1) ms, and a spectral diffusion-limited homogeneous linewidth as narrow as 4.8(3) MHz. We test the annealing of Er:CeO2 films up to 900 °C, which yields narrowing of the inhomogeneous linewidth by 20% and extension of the excited state lifetime by 40%.
Microstructural and preliminary optical and microwave characterization of erbium doped CaMoO4 thin films
This work explores erbium-doped calcium molybdate (CaMoO4) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the $\sim$1.5 μm Er3+ 4f-4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO4 formation that can be in-situ doped with Er (typically 2-100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology; while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO4 films. We perform preliminary optical and microwave characterization on the suspected Y1−Z1 transition of 2 ppm, 200 nm epitaxial CaMoO4 annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.
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.