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1. 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 (September 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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2. Continuously tunable uniaxial strain control of van der Waals heterostructure devices

   https://doi.org/10.1063/5.0211557  

   Liu, Zhaoyu; Ma, Xuetao; Cenker, John; Cai, Jiaqi; Fei, Zaiyao; Malinowski, Paul; Mutch, Joshua; Zhao, Yuzhou; Hwangbo, Kyle; Lin, Zhong; et al (May 2024, Journal of Applied Physics)

   Uniaxial strain has been widely used as a powerful tool for investigating and controlling the properties of quantum materials. However, existing strain techniques have so far mostly been limited to use with bulk crystals. Although recent progress has been made in extending the application of strain to two-dimensional van der Waals (vdW) heterostructures, these techniques have been limited to optical characterization and extremely simple electrical device geometries. Here, we report a piezoelectric-based in situ uniaxial strain technique enabling simultaneous electrical transport and optical spectroscopy characterization of dual-gated vdW heterostructure devices. Critically, our technique remains compatible with vdW heterostructure devices of arbitrary complexity fabricated on conventional silicon/silicon dioxide wafer substrates. We demonstrate a large and continuously tunable strain of up to −0.15% at millikelvin temperatures, with larger strain values also likely achievable. We quantify the strain transmission from the silicon wafer to the vdW heterostructure, and further demonstrate the ability of strain to modify the electronic properties of twisted bilayer graphene. Our technique provides a highly versatile new method for exploring the effect of uniaxial strain on both the electrical and optical properties of vdW heterostructures and can be easily extended to include additional characterization techniques. 

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3. Low-loss composite photonic platform based on 2D semiconductor monolayers

   Ipshita Datta, Sang Hoon (January 2020, Nature photographer)

   Two dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs) are promising for optical modulation, detection, and light emission since their material properties can be tuned on-demand via electrostatic doping1–21. The optical properties of TMDs have been shown to change drastically with doping in the wavelength range near the excitonic resonances22–26. However, little is known about the effect of doping on the optical properties of TMDs away from these resonances, where the material is transparent and therefore could be leveraged in photonic circuits. Here, we probe the electro-optic response of monolayer TMDs at near infrared (NIR) wavelengths (i.e. deep in the transparency regime), by integrating them on silicon nitride (SiN) photonic structures to induce strong light -matter interaction with the monolayer. We dope the monolayer to carrier densities of (7.2 ± 0.8) × 1013 cm-2, by electrically gating the TMD using an ionic liquid [P14+] [FAP-]. We show strong electro-refractive response in monolayer tungsten disulphide (WS2) at NIR wavelengths by measuring a large change in the real part of refractive index ∆n = 0.53, with only a minimal change in the imaginary part ∆k = 0.004. We demonstrate photonic devices based on electrostatically gated SiN-WS2 phase modulator with high efficiency ( ) of 0.8 V · cm. We show that the induced phase change relative to the change in absorption (i.e. ∆n/∆k) is approximately 125, that is significantly higher than the ones achieved in 2D materials at different spectral ranges and in bulk materials, commonly employed for silicon photonic modulators such as Si and III-V on Si, while accompanied by negligible insertion loss. Efficient phase modulators are critical for enabling large-scale photonic systems for applications such as Light Detection and Ranging (LIDAR), phased arrays, optical switching, coherent optical communication and quantum and optical neural networks27–30. 

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4. Directly accessing the single-soliton state of a Kerr microcomb and its universal scaling law [Invited]

   https://doi.org/10.1364/OME.541224  

   Sun, Wenhan; Li, Jingwei; Wang, Ruixuan; Li, Qing (January 2024, Optical Materials Express)

   Soliton microcombs have attracted considerable research interest due to their unique properties. Being able to directly access the single-soliton state in a Kerr microresonator simplifies the device operation and may inspire new applications. However, the general conditions leading to such operations are not well understood. In this work, we aim to elucidate the key factors enabling the direct access of the single-soliton state in a Kerr microresonator by combining the experimental results in an integrated silicon carbide platform and a comprehensive analysis based on the normalized Lugiato-Lefever equation. A general criterion linking the Kerr nonlinearity, dispersion, and thermo-optic properties has been derived, which is applicable to Kerr microresonators with varied materials, sizes, optical quality factors, and dispersion. 

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5. Recent progress in band gap engineering of two-dimensional silicon nanosheets through controlled structure and chemistry

   https://doi.org/10.35848/1347-4065/ae3619  

   Essner, Jeremy B; Jabrayilov, Maharram; Panthani, Matthew G (March 2026, Japanese Journal of Applied Physics)

   Abstract Silicon and other Group IV semiconductors are promising for next-generation optoelectronics due to their compatibility with the current microelectronic infrastructure and their unique predicted and observed electronic properties. A key challenge for realizing the potential of these materials is the indirect band gaps of silicon (and germanium), which result in poor light emission from these materials. Nanostructuring offers an intriguing path forward for overcoming this challenge. For instance, confining silicon to the nanoscale in a single dimension to yield two-dimensional silicon nanosheets results in photoluminescence quantum yields up to 10%. To further improve light emission, increased understanding of this material’s structure–property relationships is paramount. Here, we highlight our group’s recent contributions to the understanding of structure–property relationships in two-dimensional silicon nanosheets. Specifically, we discuss the impacts that structure and chemistry of solution-processed silicon nanosheets have on predicted and observed optical properties, namely, photoluminescence. 

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