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Sputtered AlN Buffer Layer for Low-Loss Crystalline AlN-on-Sapphire Integrated Photonics
Samuele Brunetta1, Samantha Sbarra2, Brandon Shuen Yi Loke2
1Laboratory of Advanced Semiconductors for Photonics and Electronics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne CH-1015, Switzerland.
ACS Photonics
|March 9, 2026
Summary
Aluminum nitride (AlN) integrated photonics research shows voids increase propagation loss. Introducing a buffer layer creates void-free AlN, significantly reducing losses for advanced photonic devices.
Area of Science:
- Materials Science
- Photonics
- Optoelectronics
Background:
- Aluminum nitride (AlN) is a promising material for integrated photonics due to its low optical losses and nonlinear properties.
- Current research often overlooks material optimization, focusing instead on applications, hindering technological maturity.
Purpose of the Study:
- To investigate the detrimental effect of voids in crystalline AlN-on-sapphire epilayers on photonic structures.
- To develop a method for creating void-free AlN layers for improved photonic device performance.
Main Methods:
- Finite-difference time-domain (FDTD) simulations to quantify void-related scattering losses.
- Epitaxial growth of AlN with a sputtered AlN buffer layer.
- Fabrication and characterization of microring resonators and dispersion-engineered waveguides.
Main Results:
- Voids in AlN epilayers cause propagation losses exceeding 30 dB cm-1 at 1550 nm.
- Void-free AlN layers achieved using a buffer layer exhibit quality factors up to 2.0 × 106 (losses < 0.2 dB cm-1).
- Void-free AlN demonstrates high-power nonlinearities, including second-harmonic and supercontinuum generation.
Conclusions:
- Voids significantly degrade AlN photonic device performance, particularly scattering losses dependent on void size and density.
- A sputtered AlN buffer layer effectively eliminates voids, enabling ultra-low loss AlN photonic integrated circuits.
- Improved AlN layers are ideal for visible and UV photonics, where scattering losses are more critical.
