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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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Crystallographic Tilt in Aluminum Gallium Nitride Epilayers Grown on Miscut Aluminum Nitride Substrates
Heteroepitaxial crystallographic tilt has been investigated as a possible strain‐relief mechanism in Al‐rich (Al>50%) AlGaN heteroepitaxial layers grown on single‐crystal (0001) AlN substrates with varying miscuts from 0.05° to 4.30°. The magnitude of the elastic lattice deformation‐induced tilt increases monotonically with the miscut angle, tightly following the Nagai tilt model. Although tilt angles as high as 0.1° are recorded, reciprocal space mapping (RSM) broadening and wafer bow measurements do not show any significant changes as a function of the heteroepitaxial tilt angle. While crystallographic tilting has been shown to be effective in controlling strain in some other heteroepitaxial systems, it does not provide any appreciable strain relief of the compressive strain in AlGaN/AlN heteroepitaxy.
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- PAR ID:
- 10377045
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- physica status solidi (RRL) – Rapid Research Letters
- Volume:
- 17
- Issue:
- 1
- ISSN:
- 1862-6254
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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