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1. High conductivity coherently strained quantum well XHEMT heterostructures on AlN substrates with delta doping

   https://doi.org/10.1063/5.0228253  

   Chen, Yu-Hsin; Encomendero, Jimy; Savant, Chandrashekhar; Protasenko, Vladimir; Xing, Huili Grace; Jena, Debdeep (September 2024, Applied Physics Letters)

   Polarization-induced two-dimensional electron gases (2DEGs) in AlN/GaN/AlN quantum well high-electron-mobility transistors on ultrawide bandgap AlN substrates offer a promising route to advance microwave and power electronics with nitride semiconductors. The electron mobility in thin GaN quantum wells embedded in AlN is limited by high internal electric field and the presence of undesired polarization-induced two-dimensional hole gases (2DHGs). To enhance the electron mobility in such heterostructures on AlN, previous efforts have resorted to thick, relaxed GaN channels with dislocations. In this work, we introduce n-type compensation δ-doping in a coherently strained single-crystal (Xtal) AlN/GaN/AlN heterostructure to counter the 2DHG formation at the GaN/AlN interface, and simultaneously lower the internal electric field in the well. This approach yields a δ-doped XHEMT structure with a high 2DEG density of ∼3.2×1013 cm−2 and a room temperature (RT) mobility of ∼855 cm2/Vs, resulting in the lowest RT sheet resistance 226.7 Ω/□ reported to date in coherently strained AlN/GaN/AlN HEMT heterostructures on the AlN platform. 

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2. Next generation electronics on the ultrawide-bandgap aluminum nitride platform

   https://doi.org/10.1088/1361-6641/abe5fd  

   Hickman, Austin Lee; Chaudhuri, Reet; Bader, Samuel James; Nomoto, Kazuki; Li, Lei; Hwang, James C. M.; Grace Xing, Huili; Jena, Debdeep (March 2021, Semiconductor Science and Technology)

   Abstract Gallium nitride high-electron-mobility transistors (GaN HEMTs) are at a point of rapid growth in defense (radar, SATCOM) and commercial (5G and beyond) industries. This growth also comes at a point at which the standard GaN heterostructures remain unoptimized for maximum performance. For this reason, we propose the shift to the aluminum nitride (AlN) platform. AlN allows for smarter, highly-scaled heterostructure design that will improve the output power and thermal management of III-nitride amplifiers. Beyond improvements over the incumbent amplifier technology, AlN will allow for a level of integration previously unachievable with GaN electronics. State-of-the-art high-current p-channel FETs, mature filter technology, and advanced waveguides, all monolithically integrated with an AlN/GaN/AlN HEMT, is made possible with AlN. It is on this new AlN platform that nitride electronics may maximize their full high-power, high-speed potential for mm-wave communication and high-power logic applications. 

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3. High-voltage kV-class AlN metal-semiconductor field-effect transistors on single-crystal AlN substrates

   https://doi.org/10.35848/1882-0786/ad85c0  

   Da, Bingcheng; Herath_Mudiyanselage, Dinusha; Wang, Dawei; He, Ziyi; Fu, Houqiang (October 2024, Applied Physics Express)

   Abstract This letter reports the demonstration and electrical characterization of high-voltage AlN metal-semiconductor field-effect transistors (MESFETs) on single-crystal AlN substrates. Compared with AlN MESFETs on foreign substrates, the AlN-on-AlN MESFETs showed high breakdown voltages of over 2 kV for drain-to-gate spacing of 15 μm and one of the highest average breakdown fields among reported AlN MESFETs. Additionally, the devices also exhibited decent drain saturation current and on/off ratio without complicated regrown or graded contact layers, which are several times higher than those of reported AlN-on-sapphire MESEFTs. This work is beneficial for the future development of ultrawide bandgap AlN power electronics. 

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4. Heteroepitaxy of N-polar AlN on C-face 4H-SiC: Structural and optical properties

   https://doi.org/10.1063/5.0168970  

   Hu, Mingtao; Wang, Ping; Wang, Ding; Wu, Yuanpeng; Mondal, Shubham; Wang, Danhao; Ahmadi, Elaheh; Ma, Tao; Mi, Zetian (December 2023, APL Materials)

   To date, it has remained challenging to achieve N-polar AlN, which is of great importance for high power, high frequency, and high temperature electronics, acoustic resonators and filters, ultraviolet (UV) optoelectronics, and integrated photonics. Here, we performed a detailed study of the molecular beam epitaxy and characterization of N-polar AlN on C-face 4H-SiC substrates. The N-polar AlN films grown under optimized conditions exhibit an atomically smooth surface and strong excitonic emission in the deep UV with luminescence efficiency exceeding 50% at room temperature. Detailed scanning transmission electron microscopy (STEM) studies suggest that most dislocations are terminated/annihilated within ∼200 nm AlN grown directly on the SiC substrate due to the relatively small (1%) lattice mismatch between AlN and SiC. The strain distribution of AlN is further analyzed by STEM and micro-Raman spectroscopy, and its impact on the temperature-dependent deep UV emission is elucidated. 

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5. Over 600 V Lateral AlN-on-AlN Schottky Barrier Diodes with Ultra-Low Ideality Factor

   https://doi.org/10.35848/1882-0786/ad5e5a  

   Herath_Mudiyanselage, Dinusha; Wang, Dawei; Da, Bingcheng; He, Ziyi; Fu, Houqiang (July 2024, Applied Physics Express)

   Abstract This letter reports the demonstration of lateral AlN Schottky barrier diodes (SBDs) on single-crystal AlN substrates by metalorganic CVD (MOCVD) with an ultra-low ideality factor (η) of 1.65, a high Schottky barrier height of 1.94 eV, a breakdown voltage (BV) of 640 V, and a record high normalizedBVby the anode-to-cathode distance. The device current was dominated by thermionic emission, while most previously reported AlN SBDs suffered from defect-induced current with higherη(>4). This work represents a significant step towards high-performance ultra-wide bandgap AlN-based high-voltage and high-power devices. 

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