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1. Engineering ultrafast photoconductive response in two-dimensional SnS2 through metal intercalation

   https://doi.org/10.1117/12.3043591  

   Khanmohammadi, Sepideh; Williams, Camille; Kushnir_Friedman, Kateryna; Grimm, Ronald L; Koski, Kristie; Titova, Lyubov V (March 2025, SPIE)

   Betz, Markus; Elezzabi, Abdulhakem Y (Ed.)

   SnS2 is a two-dimensional (2D) layered semiconductor with a visible-range bandgap (~2.3eV), high charge carrier mobility, long carrier lifetimes, and good environmental stability. This study explores the impact of zero-valent metal intercalation into the van der Waals gaps of SnS2 on charge carrier dynamics. We demonstrate that metal intercalation enhances optical absorption in the yellow-to-IR range and induces metal-dependent bandgap shifts. Time-resolved THz spectroscopy reveals that different metals uniquely influence photoconductivity dynamics: We find that intercalation with Bi, Ni, and Fe shortens the photoconductivity decay times, whereas Rh intercalation results in a slower decay. These findings highlight the potential of metal intercalation to tailor SnS2 properties for diverse applications, from solar energy conversion to high-speed photodetectors. 

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2. DNA‐Based Strategies for Site‐Specific Doping

   https://doi.org/10.1002/adfm.202005940  

   Bai, Ruobing; Du, Yanhao; Xu, Anqin; Hu, Yang; Erickson, John R.; Hui, Liwei; Chen, Jun; Xiong, Feng; Liu, Haitao (September 2020, Advanced Functional Materials)

   Abstract The development of novel doping strategies compatible with high‐resolution patterning and low cost, large‐scale manufacturing is critical to the future development of electronic devices. Here, an approach to achieve nanoscale site‐specific doping of Si wafer using DNA as both the template and the dopant carrier is reported. Upon thermal treatment, the phosphorous atoms in the DNA diffuse into Si wafer, resulting in doping within the region right around the DNA template. A doping length of 30 nm is achieved for 10 s of thermal treatment at 1000 °C. Prototype field effect transistors are fabricated using the DNA‐doped Si substrate; the device characteristics confirmed that the Si is n‐doped. It is also shown that this approach can be extended to achieve both n‐type and p‐type site‐specific doping of Si by using DNA nanostructures to pattern self‐assembled monolayers. This work shows that the DNA template is a dual‐use template that can both pattern Si and deliver dopants. 

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3. On-chip wavelength division multiplexing filters using extremely efficient gate-driven silicon microring resonator array

   https://doi.org/10.1038/s41598-023-32313-0  

   Hsu, Wei-Che; Nujhat, Nabila; Kupp, Benjamin; Conley, Jr, John F.; Wang, Alan X. (March 2023, Scientific Reports)

   Abstract Silicon microring resonators (Si-MRRs) play essential roles in on-chip wavelength division multiplexing (WDM) systems due to their ultra-compact size and low energy consumption. However, the resonant wavelength of Si-MRRs is very sensitive to temperature fluctuations and fabrication process variation. Typically, each Si-MRR in the WDM system requires precise wavelength control by free carrier injection using PIN diodes or thermal heaters that consume high power. This work experimentally demonstrates gate-tuning on-chip WDM filters for the first time with large wavelength coverage for the entire channel spacing using a Si-MRR array driven by high mobility titanium-doped indium oxide (ITiO) gates. The integrated Si-MRRs achieve unprecedented wavelength tunability up to 589 pm/V, or V_πL of 0.050 V cm with a high-quality factor of 5200. The on-chip WDM filters, which consist of four cascaded ITiO-driven Si-MRRs, can be continuously tuned across the 1543–1548 nm wavelength range by gate biases with near-zero power consumption. 

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4. Hot carrier transfer from plasmon decay in Ag ₂₀ at H–Si(111) surface: real-time TDDFT simulation in Wannier gauge

   https://doi.org/10.1088/1361-648X/ad8b8e  

   Bost, John L; Shepard, Christopher; Kanai, Yosuke (November 2024, Journal of Physics: Condensed Matter)

   Abstract Plasmon decay is believed to play an essential role in inducing hot carrier transfer at the interfaces between plasmonic nanoparticles and semiconductor surfaces. In this work, we employ real-time time-dependent density functional theory (RT-TDDFT) simulation in the Wannier gauge to gain quantum-mechanical insights into the nonlinear dynamics of the plasmon decay in the Ag₂₀nanoparticle at a semiconductor surface. The first-principles simulations show that the plasmon decay is more than two times faster when the Ag₂₀nanoparticle is adsorbed on a hydrogen-terminated Si(111) surface, taking place within 100 femtoseconds of the plasmon excitation. Hot carrier transfer across the interface is observed as the plasmon decay takes place, and nearly 30% of holes are generated deep in the valence band of the semiconductor surface. The use of Wannier gauge in RT-TDDFT simulation is particularly convenient for gaining quantum-mechanical insights into non-equilibrium electron dynamics in complex heterogeneous systems. 

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5. Achieving semi-metallic conduction in Al-rich AlGaN: Evidence of Mott transition

   https://doi.org/10.1063/5.0210143  

   Mondal, Shubham; Kezer, Pat; Wang, Ding; Tanim, Md_Mehedi Hasan; Heron, John T; Mi, Zetian (June 2024, Applied Physics Letters)

   The development of high performance wide-bandgap AlGaN channel transistors with high current densities and reduced Ohmic losses necessitates extremely highly doped, high Al content AlGaN epilayers for regrown source/drain contact regions. In this work, we demonstrate the achievement of semi-metallic conductivity in silicon (Si) doped N-polar Al0.6Ga0.4N grown on C-face 4H-SiC substrates by molecular beam epitaxy. Under optimized conditions, the AlGaN epilayer shows smooth surface morphology and a narrow photoluminescence spectral linewidth, without the presence of any secondary peaks. A favorable growth window is identified wherein the free electron concentration reaches as high as ∼1.8 × 1020 cm−3 as obtained from Hall measurements, with a high mobility of 34 cm2/V·s, leading to a room temperature resistivity of only 1 mΩ·cm. Temperature-dependent Hall measurements show that the electron concentration, mobility, and sheet resistance do not depend on temperature, clearly indicating dopant Mott transition to a semi-metallic state, wherein the activation energy (Ea) falls to 0 meV at this high value of Si doping for the AlGaN films. This achievement of semi-metallic conductivity in Si doped N-polar high Al content AlGaN is instrumental for advancing ultrawide bandgap electronic and optoelectronic devices. 

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