V. Kaliuzhnyi, O. Liubchenko, M. Tymochko, Y. Olikh, V. Kladko, and A. Belyaev, “Investigation of Traps in AlGaN/GaN Heterostructures by Ultrasonic Vibrations”, Ukr. J. Phys., vol. 66, no. 12, p. 1058, Dec. 2021.