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1. Thermo-optic properties of silicon-rich silicon nitride for on-chip applications

   https://doi.org/10.1364/OE.396969  

   Nejadriahi, Hani; Friedman, Alex; Sharma, Rajat; Pappert, Steve; Fainman, Yeshaiahu; Yu, Paul (August 2020, Optics Express)

   We demonstrate the thermo-optic properties of silicon-rich silicon nitride (SRN) films deposited using plasma-enhanced chemical vapor deposition (PECVD). Shifts in the spectral response of Mach-Zehnder interferometers (MZIs) as a function of temperature were used to characterize the thermo-optic coefficients of silicon nitride films with varying silicon contents. A clear relation is demonstrated between the silicon content and the exhibited thermo-optic coefficient in silicon nitride films, with the highest achievable coefficient being as high as (1.65±0.08) ×10⁻⁴K^-1. Furthermore, we realize an SRN multi-mode interferometer (MMI) based thermo-optic switch with over 20 dB extinction ratio and total power consumption for two-port switching of 50 mW. 

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2. Demonstration of 4H-silicon carbide on an aluminum nitride integrated photonic platform

   https://doi.org/10.1364/OL.521157  

   Wang, Ruixuan; Li, Jingwei; Cai, Lutong; Li, Qing (January 2024, Optics Letters)

   The existing silicon-carbide-on-insulator photonic platform utilizes a thin layer of silicon dioxide under silicon carbide (SiC) to provide optical confinement and mode isolation. Here, we replace the underneath silicon dioxide layer with 1-µm-thick aluminum nitride and demonstrate a 4H-silicon-carbide-on-aluminum-nitride integrated photonic platform for the first time to our knowledge. Efficient grating couplers, low-loss waveguides, and compact microring resonators with intrinsic quality factors up to 210,000 are fabricated. In addition, by undercutting the aluminum nitride layer, the intrinsic quality factor of the silicon carbide microring is improved by nearly one order of magnitude (1.8 million). Finally, an optical pump–probe method is developed to measure the thermal conductivity of the aluminum nitride layer, which is estimated to be over 30 times of that of silicon dioxide. 

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3. Transmission Electron Microscopy Characterizations of Local Amorphization of Single Crystal Silicon by Nanosecond Pulsed Laser Direct Writing

   https://doi.org/10.1002/adem.202301377  

   Trinh, Lanh; Wang, Xinya; Zhang, Xiang; Hosseini-Zavareh, Sajed; Mao, Aofei; Yu, Xiaoming; Lei, Shuting; Cui, Bai (December 2023, Advanced Engineering Materials)

   The concept for fabrication of waveguides by an in‐volume laser direct writing in single‐crystal silicon is explored using a nanosecond pulse laser. The key innovation of this technology relies on the generation of amorphous silicon, which has a higher refractive index than that of crystalline silicon. Herein, transmission electron microscopy (TEM) together with selected area electron diffraction (SAED) and high‐resolution TEM (HRTEM) characterizations are used to better understand the microstructural evolutions. TEM images reveal the core‐shell structures, while SAED patterns and HRTEM directly observe the presence of amorphous silicon in the core surrounded by a crystalline silicon shell. With a lower laser scanning speed, a higher density of defects yet less amorphous silicon is formed by laser direct writing. 

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4. Creating Single Color Centers in Nanodiamonds with Ion Implantation

   https://doi.org/10.1364/CLEO_FS.2023.FTu3C.1  

   Xu, Xiaohui; Martin, Zachariah O.; Titze, Michael; Wang, Yongqiang; Sychev, Demid; Henshaw, Jacob; Lagutchev, Alexei S.; Htoon, Han; Bielejec, Ed; Bogdanov, Simeon; et al (January 2023, Creating Single Color Centers in Nanodiamonds with Ion Implantation)

   We report the first demonstration of single silicon vacancy center creation in 20 nm nanodiamonds using silicon ion implantation combined with thermal annealing. Room-temperature single photon emission with linewidth below 10 nm is observed. 

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5. Silicon‐On‐Silicon Carbide Platform for Integrated Photonics

   https://doi.org/10.1002/adom.202401101  

   DeVault, Clayton_T; Deckoff‐Jones, Skylar; Liu, Yuzi; Hammock, Ian_N; Sullivan, Sean_E; Dibos, Alan; Sorce, Peter; Orcutt, Jason; Awschalom, David_D; Heremans, F_Joseph; et al (August 2024, Advanced Optical Materials)

   Abstract Silicon carbide (SiC)'s nonlinear optical properties and applications to quantum information have recently brought attention to its potential as an integrated photonics platform. However, despite its many excellent material properties, such as large thermal conductivity, wide transparency window, and strong optical nonlinearities, it is generally a difficult material for microfabrication. Here, it is shown that directly bonded silicon‐on‐silicon carbide can be a high‐performing hybrid photonics platform that does not require the need to form SiC membranes or directly pattern in SiC. The optimized bonding method yields defect‐free, uniform films with minimal oxide at the silicon–silicon–carbide interface. Ring resonators are patterned into the silicon layer with standard, complimentary metal–oxide–semiconductor (CMOS) compatible (Si) fabrication and measure room‐temperature, near‐infrared quality factors exceeding 10⁵. The corresponding propagation loss is 5.7 dB cm⁻¹. The process offers a wafer‐scalable pathway to the integration of SiC photonics into CMOS devices. 

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