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Harnessing Atomic Layer Deposition and Diffusion to Spatially Localize Rare-Earth Ion Emitters

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 Y2O3 film or a Y2SiO5 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 Eu2O3/Y2O3/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 Eu2O3 ALD film into a single-crystalline
substrate of Y2SiO5 (YSO), a technologically
relevant material system for quantum applications. We determine the
Eu3+ diffusion coefficients in both cases and show that
diffusion starts at 950 °C in the polycrystalline Y2O3 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.