Pseudomorphic growth of thick Al0.6Ga0.4N epilayers on AlN substrates

We report on the absence of strain relaxation mechanism in Al0.6Ga0.4N epilayers grown (0001) AlN substrates for thickness as large 3.5 μm, three-orders magnitude beyond Matthews–Blakeslee critical formation misfit dislocations (MDs). A steady-state compressive stress 3–4 GPa was observed throughout AlGaN growth leading to a lattice bow (a radius curvature 0.5 m−1) thickest sample. Despite mismatch-induced energy, exhibited smooth and crack-free surface morphology. These results point presence barrier nucleation MDs Al-rich epilayers. Compositionally graded layers were investigated potential relief by intentional introduction MDs. While abetted MD formation, inadequate length these correlated with insignificant relaxation. This study emphasizes importance developing management strategies implementation single-crystal substrate platform III-nitride deep-UV optoelectronics power electronics.