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1. Writing above the bandgap

   https://doi.org/10.1038/s41563-023-01561-w  

   Majety, Sridhar; Radulaski, Marina (June 2023, Nature Materials)
2. Photonic bandgap microcombs at 1064 nm

   https://doi.org/10.1063/5.0191602  

   Spektor, Grisha; Zang, Jizhao; Dan, Atasi; Briles, Travis C; Brodnik, Grant M; Liu, Haixin; Black, Jennifer A; Carlson, David R; Papp, Scott B (February 2024, APL Photonics)

   Microresonator frequency combs and their design versatility have revolutionized research areas from data communication to exoplanet searches. While microcombs in the 1550 nm band are well documented, there is interest in using microcombs in other bands. Here, we demonstrate the formation and spectral control of normal-dispersion dark soliton microcombs at 1064 nm. We generate 200 GHz repetition rate microcombs by inducing a photonic bandgap of the microresonator mode for the pump laser with a photonic crystal. We perform the experiments with normal-dispersion microresonators made from Ta2O5 and explore unique soliton pulse shapes and operating behaviors. By adjusting the resonator dispersion through its nanostructured geometry, we demonstrate control over the spectral bandwidth of these combs, and we employ numerical modeling to understand their existence range. Our results highlight how photonic design enables microcomb spectra tailoring across wide wavelength ranges, offering potential in bioimaging, spectroscopy, and photonic-atomic quantum technologies. 

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3. Large bandgap of pressurized trilayer graphene

   https://doi.org/https://doi.org/10.1073/pnas.1820890116  

   Ke, Feng; Chen, Yabin; Yin, Ketao; Yan, Jiejuan; Zhang, Hengzhong; Liu, Zhenxian; Tse, John; Wu, Junqiao; Mao, Ho-Kwang; Chen, Bin. (May 2019, Proceedings of the National Academy of Sciences of the United States of America)

   Graphene-based nanodevices have been developed rapidly and are now considered a strong contender for postsilicon electronics. However, one challenge facing graphene-based transistors is opening a sizable bandgap in graphene. The largest bandgap achieved so far is several hundred meV in bilayer graphene, but this value is still far below the threshold for practical applications. Through in situ electrical measurements, we observed a semiconducting character in compressed trilayer graphene by tuning the interlayer interaction with pressure. The optical absorption measurements demonstrate that an intrinsic bandgap of 2.5 ± 0.3 eV could be achieved in such a semiconducting state, and once opened could be preserved to a few GPa. The realization of wide bandgap in compressed trilayer graphene offers opportunities in carbon-based electronic devices. 

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4. Quantum Channel Extreme Bandgap AlGaN HEMT

   https://doi.org/10.3390/mi15111384  

   Shur, Michael; Simin, Grigory; Hussain, Kamal; Mamun, Abdullah; Chandrashekhar, M_V S; Khan, Asif (November 2024, Micromachines)

   Wengang, Bi; Haiding, Sun (Ed.)

   An extreme bandgap Al0.64Ga0.36N quantum channel HEMT with Al0.87Ga0.13N top and back barriers, grown by MOCVD on a bulk AlN substrate, demonstrated a critical breakdown field of 11.37 MV/cm—higher than the 9.8 MV/cm expected for the channel’s Al0.64Ga0.36N material. We show that the fraction of this increase is due to the quantization of the 2D electron gas. The polarization field maintains electron quantization in the quantum channel even at low sheet densities, in contrast to conventional HEMT designs. An additional increase in the breakdown field is due to quantum-enabled real space transfer of energetic electrons into high-Al barrier layers in high electric fields. These results show the advantages of the quantum channel design for achieving record-high breakdown voltages and allowing for superior power HEMT devices. 

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5. Infrared photodetection using narrow bandgap conjugated polymers

   https://doi.org/10.1117/12.3000525  

   Azoulay, Jason D (March 2024, Proceedings SPIE)

   Rau, Ileana; Sugihara, Okihiro; Shensky, William M (Ed.)

   Low-energy, infrared (IR) photodetection forms the foundation for industrial, scientific, energy, medical, and defense applications. State-of-the-art technologies suffer from limited modularity, intrinsic fragility, high-power consumption, require cooling, and are largely incompatible with integrated circuit technologies. Conjugated polymers offer low-cost and scalable fabrication, solution processability, room temperature operation, and other attributes that are not available using current technologies. Here, we demonstrate new materials and device paradigms that enable an understanding of emergent light-matter interactions and optical to electrical transduction of IR light. Photodiodes show a response to 2.0 μm, while photoconductors respond across the near- to long-wave infrared (1–14 µm). Fundamental investigations of polymer and device physics have resulted in improving performance to levels now matching commercial inorganic detectors. This is the longest wavelength light detected for organic materials and the performance exceeds graphene at longer wavelengths. Photoconductors outperform their inorganic counterparts and operate at room temperature with higher response speeds. 

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