AlN is a promising material for integrated quantum photonics due to its broad transparency window, its compatibility with CMOS technology, and the possibility to host localized light emitters acting as single photon sources. However, little is understood yet about the microscopic nature and formation mechanisms of these light emitters. In this contribution, we demonstrate that their formation efficiency depends significantly on the growth conditions of the AlN thin film. We reveal that localized light emitters with distinct zero-phonon lines in the 600--800~nm range can be efficiently formed in epitaxial AlN thin films grown under N-rich conditions by exposing the AlN to a post-growth treatment consisting in a proton irradiation followed by an annealing process. In contrast, the density of light emitters formed in AlN grown under Al-rich conditions remains low, even after the thin films have been exposed to the post-growth treatment. These results open a pathway toward a better understanding of the microscopic nature of these light emission centers, as well as their engineered integration as quantum light sources in AlN-based optomechanical platforms.
AlN is a promising material for integrated quantum photonics due to its broad transparency window, its compatibility with CMOS technology, and the possibility to host localized light emitters acting as single photon sources. However, little is understood yet about the microscopic nature and formation mechanisms of these light emitters. In this contribution, we demonstrate that their formation efficiency depends significantly on the growth conditions of the AlN thin film. We reveal that localized light emitters with distinct zero-phonon lines in the 600--800~nm range can be efficiently formed in epitaxial AlN thin films grown under N-rich conditions by exposing the AlN to a post-growth treatment consisting in a proton irradiation followed by an annealing process. In contrast, the density of light emitters formed in AlN grown under Al-rich conditions remains low, even after the thin films have been exposed to the post-growth treatment. These results open a pathway toward a better understanding of the microscopic nature of these light emission centers, as well as their engineered integration as quantum light sources in AlN-based optomechanical platforms.
Generation, manipulation and detection of quantum states of light lies at the heart of modern physical sciences. There is a global effort on discovering material platforms that will result in a quantum advantage over the classical implementations for certain useful problems in cryptography, communications and computing. An avenue being explored is the generation of single-photons for practical quantum computing and communications applications. Aluminium nitride (AlN) is one of the promising materials as it is compatible with CMOS processes, hosts crystal defects as qubit candidates within its wide bandgap and offers respectable second- and third-order nonlinearity coefficients. Combined with its high refractive index, large piezoelectric coefficients and considerable thermal conductivity, it is an ideal device platform for controllable and deterministic single-photon source implementations. In this thesis, I will present my work on creation of single-photon emitters in AlN through ion implantation and annealing, followed by the characterisation of the created defects via confocal microscopy. A design and fabrication methodology for increasing the brightness of such emitters through micro/nanofabrication will be explored, and preliminary results on brightness enhancement from native defects in AlN will be presented. A 4-inch process for AlN-on-sapphire platform will be outlined with the aim of providing a scalable integrated photonics platform for possible single-photon source implementations in AlN. This work builds a foundation of theoretical and experimental basis for future studies, both for crystal defects in AlN, as well as four-wave mixing AlN PICs for high-performance single-photon generation.
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.
Controlled growth of rare-earth-doped TiO2 thin films on III-V semiconductors for hybrid quantum photonic interfaces
Quantum photonic networks require two distinct functionalities: bright single-photon sources and long-lived quantum memories. III-V semiconductor quantum dots excel as deterministic and coherent photon emitters, while rare-earth ions such as erbium (Er3+) in crystalline oxides offer exceptional spin and optical coherence at telecom wavelengths. Combining these systems and their functionalities via direct epitaxy is challenging due to lattice mismatch and incompatible growth conditions. Here we demonstrate low-temperature pulsed laser deposition of Er3+-doped TiO2 thin films directly on GaAs and GaSb substrates. Controlled surface preparation with an arsenic cap and an oxygen-deficient buffer layer enables the growth of epitaxial anatase TiO2 (001) at 390oC with sub-300 pm surface roughness, while avoiding interface degradation. In contrast, high-temperature oxide desorption or growth temperatures drive the transition to rough, polycrystalline rutile film, as confirmed by transmission electron microscopy. Minimal coincident interface area (MCIA) modeling explains the orientation-selective growth on GaAs and GaSb. Raman and cryogenic photoluminescence excitation spectroscopy verify the crystal phase and optical activation of Er3+ ions. This multi-parameter growth strategy helps preserve III-V quantum dot functionality and yields smooth surfaces suitable for low-loss nanophotonic structures. Our results establish a materials platform for monolithically integrating rare-earth quantum memories with semiconductor photon sources, paving the way toward scalable hybrid quantum photonic chips.
Single photons are very attractive for quantum information processing, given their long coherence time and their ability to carry information in many degrees of freedom. A current challenge is the generation of single photons in a photonic chip in order to scale up the complexity of quantum operations. Solid state emitters could offer this possibility. Quantum dots are one promising approach, but photons produced by different dots are generally distinguishable. Nitrogen-vacancy (N-V) centres in diamond are also promising, however it is challenging to place these in photonic circuits and the emitted photons have many frequencies. By contrast, dibenzoterrylene (DBT) molecules embedded in a thin film of anthracene (AC) at cryogenic temperatures produce a high yield of indistinguishable photons [1, 2]. DBT acts as a two-level system with a narrow 30 MHz near-infrared (785 nm) zero-phonon line [1]. We have proposed that a DBT molecule, deposited in the vicinity of a nanoscale waveguide, could emit these photons efficiently into the waveguide [3]. Conventional spin-coating methods [1] do not offer sufficient control over the surface coverage and the morphology of the AC crystal for deposition on photonic structures, while crystals grown with sublimation are too thick. Another method is needed.
Integrated quantum photonics holds significant promise for scalable photonic quantum information processing, quantum repeaters, and quantum networks, but its development is hindered by the mismatch between materials hosting high-quality quantum emitters and those compatible with mature photonic technologies. Heterogeneous integration offers a potential solution to this challenge, yet practical implementations have been limited by inevitable insertion losses at material interfaces. Here, we present a self-aligned heterogeneous quantum photonic integration approach that can deterministically achieve near-unity coupling efficiency at the interface. To showcase our approach, we demonstrate Purcell enhancement of a silicon vacancy (SiV) center in diamond induced by a heterogeneous photonic crystal cavity defined by titanium dioxide (TiO2), as well as optical spin control and readout via a TiO2 photonic circuit. We further show that, when combined with inverse photonic design, our approach enables efficient and broadband collection of single photons from a color center into a heterogeneous waveguide. Our approach is not restricted to SiV centers or TiO2; it can be broadly applied to integrate diverse solid-state quantum emitters with thin-film photonic devices where conformal deposition is possible. Together, these results establish a practical route to scalable quantum photonic integrated circuits that combine high-quality quantum emitters with technologically mature photonic platforms.
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.