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1. Pseudomorphic growth of thick Al _0.6 Ga _0.4 N epilayers on AlN substrates

   https://doi.org/10.1063/5.0092937  

   Rathkanthiwar, Shashwat; Houston Dycus, J.; Mita, Seiji; Kirste, Ronny; Tweedie, James; Collazo, Ramon; Sitar, Zlatko (May 2022, Applied Physics Letters)

   We report on the absence of strain relaxation mechanism in Al 0.6 Ga 0.4 N epilayers grown on (0001) AlN substrates for thickness as large as 3.5  μm, three-orders of magnitude beyond the Matthews–Blakeslee critical thickness for the formation of misfit dislocations (MDs). A steady-state compressive stress of 3–4 GPa was observed throughout the AlGaN growth leading to a large lattice bow (a radius of curvature of 0.5 m −1 ) for the thickest sample. Despite the large lattice mismatch-induced strain energy, the epilayers exhibited a smooth and crack-free surface morphology. These results point to the presence of a large barrier for nucleation of MDs in Al-rich AlGaN epilayers. Compositionally graded AlGaN layers were investigated as potential strain relief layers by the intentional introduction of MDs. While the graded layers abetted MD formation, the inadequate length of these MDs correlated with insignificant strain relaxation. This study emphasizes the importance of developing strain management strategies for the implementation of the single-crystal AlN substrate platform for III-nitride deep-UV optoelectronics and power electronics. 

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2. Record >10 MV/cm mesa breakdown fields in Al _0.85 Ga _0.15 N/Al _0.6 Ga _0.4 N high electron mobility transistors on native AlN substrates

   https://doi.org/10.1063/5.0083966  

   Khachariya, Dolar; Mita, Seiji; Reddy, Pramod; Dangi, Saroj; Dycus, J. Houston; Bagheri, Pegah; Breckenridge, M. Hayden; Sengupta, Rohan; Rathkanthiwar, Shashwat; Kirste, Ronny; et al (April 2022, Applied Physics Letters)

   The ultra-wide bandgap of Al-rich AlGaN is expected to support a significantly larger breakdown field compared to GaN, but the reported performance thus far has been limited by the use of foreign substrates. In this Letter, the material and electrical properties of Al 0.85 Ga 0.15 N/Al 0.6 Ga 0.4 N high electron mobility transistors (HEMT) grown on a 2-in. single crystal AlN substrate are investigated, and it is demonstrated that native AlN substrates unlock the potential for Al-rich AlGaN to sustain large fields in such devices. We further study how Ohmic contacts made directly to a Si-doped channel layer reduce the knee voltage and increase the output current density. High-quality AlGaN growth is confirmed via scanning transmission electron microscopy, which also reveals the absence of metal penetration at the Ohmic contact interface and is in contrast to established GaN HEMT technology. Two-terminal mesa breakdown characteristics with 1.3  μm separation possess a record-high breakdown field strength of ∼11.5 MV/cm for an undoped Al 0.6 Ga 0.4 N-channel layer. The breakdown voltages for three-terminal devices measured with gate-drain distances of 4 and 9  μm are 850 and 1500 V, respectively. 

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3. Temperature Effect on Performance of Enhancement Mode Al _0.4 Ga _0.6 n-Channel Moshfets with Hybrid Oxide

   https://doi.org/10.1149/MA2021-01331071mtgabs  

   Mollah, Shahab; Gaevski, Mikhail; Hussain, Kamal; Mamun, Abdullah; Chandrashekhar, Mvs; Simin, Grigory; Khan, Asif (May 2021, ECS Meeting Abstracts)
4. Band alignment of B _0.14 Al _0.86 N/Al _0.7 Ga _0.3 N heterojunction

   https://doi.org/10.1063/1.4999249  

   Sun, Haiding; Park, Young Jae; Li, Kuang-Hui; Torres Castanedo, C. G.; Alowayed, Abdulmohsen; Detchprohm, Theeradetch; Dupuis, Russell D.; Li, Xiaohang (September 2017, Applied Physics Letters)
5. Bandgap narrowing and Mott transition in Si-doped Al _0.7 Ga _0.3 N

   https://doi.org/10.1063/1.5086052  

   Bharadwaj, Shyam; Islam, S. M.; Nomoto, Kazuki; Protasenko, Vladimir; Chaney, Alexander; Xing, Huili; Jena, Debdeep (March 2019, Applied Physics Letters)