12/21 Seminar Speech

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SpeakerProfessor Yi-Chia Chou

OrganizationDepartment of Electrophysics, National Chiao Tung University  

TopicDirect Growth of Flexible GaN Film via van der Waals Epitaxy

 Date10:20 am 2020.12.21

LocationRoom 203, College of Engineering

Abstract;A flexible gallium nitride thin film was obtained on mica through van der Waals epitaxy. A hydride vapor phase epitaxy was applied to fabricate such flexible GaN thin film directly on substrate suing an optimized two-step growing process to form LT-GaN and HT-GaN sequentially. The interfacial stress caused by the mismatches of thermal expansion coefficient and lattice were significantly reduced via van der Waals epitaxy and the proposed two-step growth. A critical (minimum) growth pressure was found to grow the HT-GaN. The optical performance was controlled by interface and surface roughness. For poor-quality LT-GaN, it quickly decomposed during HT-GaN growth and induced high density of defects near the LT-GaN/HT-GaN interface. The defects then caused the GaN film non-transparent. The surface roughness also controlled the transmittance. In the measurement region, the average transmittance decreased linearly as the GaN surface became rougher. A reliability test was approached where the strong bending caused slight PL peak shift, but did not significantly reduced the peak intensity. Thus, such direct grown GaN film on F-mica substrate can be evaluated as a reliable optical device.