Improving the Luminescent Properties of Atomic Layer Deposition Eu:Y₂O₃ Thin Films through Optimized Thermal Annealing

Abstract

Crystalline rare‐earth (RE)‐doped Y2O3 films are an attractive system for a wide range of photonics applications including quantum technologies which aim at harnessing optical or spin transitions with long coherence times to achieve new functionalities such as quantum storage or information processing. Herein, atomic layer deposition (ALD) of Eu‐doped Y2O3 thin films with improved optical properties is presented. A crucial post‐treatment step to obtain high‐quality films is annealing at elevated temperatures (>900 °C). However, the main drawback of this approach is the formation of unwanted parasitic phases due to reaction at the interface with the substrate, especially with silicon. In this article, this issue is discussed for different kinds of substrates and buffer layers. The use of such modified substrates allows advantageously extending the maximum thermal treatment up to 1150 °C without being limited by interface reactions. It is demonstrated that the emission of the 5D0 → 7F2 transition for Eu3+ in Y2O3 film can be as narrow as that of bulk materials when optimized thermal treatments and a thin undoped Y2O3 buffer layer are used. Thus, a versatile method to reduce the impact of the substrate–film interface on the optical properties is proposed.

Chemically vapor deposited Eu3+:Y2O3 thin films as a material platform for quantum technologies

“…However, ALD is limited to a restricted low-temperature window that does not easily allow for the synthesis of epitaxial oxide films. High temperature post-treatments (950-1050 °C) can partially improve the structural order, but they lead to the formation of parasitic interfacial phases 27 as well as unwanted dopant diffusion 28 which may be a limiting factor especially on silicon substrates. Chemical Vapour Deposition (CVD) offers an interesting approach for the deposition of high quality epitaxial RE oxide films due to the possibility to grow under a more flexible range of conditions and higher temperatures 29 .…”

Controlling the interfacial reactions and environment of rare-earth ions in thin oxide films towards wafer-scalable quantum technologies

“…In order to keep the curative aspect of annealing while limiting disorder 17,26,30,52 , the Eu ions of interest in the active layer were protected with undoped Y 2 O 3 buffer and a cap layers of similar thicknesses of 80 nm (Fig. 5-a).…”

“…Beyond the development of those systems, a compact, waferscalable thin film platform would be a great asset 19 to develop new functionalities including the coupling of a RE doped film with cavities 20 , graphene layer 21 or into a waveguide structure 22 . In addition, such thin films could be compatible with silicon photonic technologies 23,24 and they favor an efficient control and spatial localization of dopants within the crystalline matrix 25,26 with applications in quantum sensing 27 or single ion spectroscopy for quantum computing 28,29 . Currently, the main challenge in nanometer thin films is to preserve the extremely narrow optical and spin homogeneous linewidth related to long coherence properties of RE ions against the presence of surface defects and impurities.…”

“…The temperature and duration of this post treatment are key parameters since thermallyactivated diffusion of impurities or reaction with the substrate are known to take place. For example, although post-growth thermal annealing of ALD Eu:Y 2 O 3 films on silicon substrates allowed obtaining narrow and well-resolved emission lines, annealing temperatures (T A ) are limited to less than 950 °C before reaction with silicon substrate leads to parasitic silicate phases 23,26,34 .…”

Tuning of Emission Wavelength of CaS:Eu by Addition of Oxygen Using Atomic Layer Deposition

“…However, using ALD, the spatial distance between the luminescent centers can be controlled. The distance is restrained by the steric hindrance effect of the ligands [5][6][7][8]. With this distribution engineering procedure, higher doping concentrations can be achieved in comparison to other fabrication techniques [7], which may reflect in higher luminance values.…”