Abstract
Germanium on silicon (GOS) is an excellent platform for non-dispersive infrared sensing (NDIR) due to its broad mid-infrared (mid-IR) transparency. However, its optical waveguide propagation loss as a photonic sensing medium and its susceptibility to oxidation are concerns to be addressed. Herein, we study the effect of annealing GOS waveguide devices under forming gas and passivation using atomic layer deposition (ALD) of aluminum oxide (Al2O3) and aluminum nitride (AlN) on waveguide loss. Our findings showed that annealing helped reduce propagation loss as high as 17x at wavelength of ~ 5.85 μm and passivation with AlN was effective in minimising oxidation of germanium (Ge) in ambient, albeit at the expense of higher waveguide loss originating from the MIR absorption in the AlN film itself. Nevertheless, these results provide insights towards improving the performance and robustness of a GOS waveguide-based sensor.
Data availability
The data set generated or analyzed during the course of the study are available from the corresponding author upon reasonable request.
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Acknowledgements
This work is supported by Institute of Microelectronics, A*STAR (Agency for Science, Technology and Research) and A*STAR (C233312034) for design and testing, the National Research Foundation, Singapore, and A*STAR, Singapore under its Low-Carbon Energy Research (LCER) Funding Initiative (FI) (Award no.: U2102d2012) for fabrication and LCER Phase 2 (Award no.: U2303D4001) for design and A*STAR (C220415015) for fabrication.
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R. C. F. A. fabricated the device. L. Y. M. T. and L. W. L. designed the device and guided the device fabrication. L. Y. M. T. and D. K. T. N. proposed further post processing treatments to improve the propagation loss and passivate the device. J. S. G. processed the devices for annealing under forming gas and Z. C. passivate the chips by ALD using Al2O3 and AlN films. R. C. F. A. and L. Y. M. T. conducted device measurements and analysis. A. W. K. F. guided in the device measurement. R. C. F. A., L. Y. M. T., L. W. L. and A. S. K. T. wrote the manuscript. The manuscript was written with the contributions of all authors. All authors have given approval to the final version of the manuscript.
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Ang, R.C.F., Goh, J.S., Tobing, L.Y.M. et al. Annealing and passivation study of germanium on silicon (GOS) mid-infrared waveguide for sensing applications. Sci Rep (2026). https://doi.org/10.1038/s41598-026-35766-1
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DOI: https://doi.org/10.1038/s41598-026-35766-1
