Laser-Inscribed Flexible Bragg Gratings Containing Silicon Oxynitride Doped Silicon Thin Film for Authentication Applications and Their Electronic and Structural Properties from X-Ray Absorption Spectroscopy and Ab Initio Calculations

The incorporation of silicon oxynitride (SiON) into silicon (Si) allows us to create a unique material in the field of Si photonics with tunable optical properties [1]. Conventional materials like SixN<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</inf>, SiOxN<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</inf>, and Si-rich Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>N<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> are utilized for their mechanical robustness, thermal stability, chemical resistance, electrical insulation, and optical transparency [2], [3]. This study presents innovative advancements in silicon photonics through the synthesis of silicon oxynitride-doped silicon (SiON-doped Si) on flexible substrates, enabling the development of distributed Bragg gratings (BGs) for anti-counterfeiting applications. Utilizing a modified plasma-enhanced chemical vapor deposition system, we achieved low-temperature fabrication of SiON-doped Si, which exhibits a refractive index range from 2.1 to 2.5 at the wavelength of 1310 nm and unique photosensitivity properties across various wavelengths. Our research demonstrates that these flexible BGs can be inscribed with femtosecond laser light, allowing for the encoding of micro-information that is observable under specific viewing angles and light conditions due to change in the absorption of the photosensitive SiON-doped Si thin films layers. The structural integrity and optical characteristics of the BGs were thoroughly analyzed using soft X-ray absorption spectroscopy, Raman spectroscopy, and grazing incidence X-ray diffraction, confirming their potential for high-performance applications in lasers and spectrometers. The findings indicate that the incorporation of SiON-doped Si in wearable technologies not only enhances authentication mechanisms but also opens new avenues for versatile optical devices. This work lays the groundwork for future explorations into advanced materials systems in silicon photonics [4], emphasizing the role of SiON-doped Si in enhancing security features in consumer products.