Strain Management of AlGaN-Based Distributed Bragg Reflectors With GaN Interlayer Grown by Metalorganic Chemical Vapor Deposition

We report the crack-free growth of a 45-pair Al_0.30Ga_0.70N/Al_0.04Ga_0.96N distributed Bragg reflector (DBR) on 2 in. diameter AlN/sapphire template by metalorganic chemical vapor deposition. To mitigate the cracking issue originating from the tensile strain of Al_0.30Ga_0.70N on GaN, an AlN template was employed in this work. On the other hand, strong compressive strain experienced by Al_0.04Ga_0.96N favors 3D island growth, which is undesired. We found that inserting an 11 nm thick GaN interlayer upon the completion of AlN template layer properly managed the strain such that the Al_0.30Ga_0.70N/Al_0.04Ga_0.96N DBR was able to be grown with an atomically smooth surface morphology. Smooth surfaces and sharp interfaces were observed throughout the structure using high-angle annular dark-field imaging in the STEM. The 45-pair AlGaN-based DBR provided a peak reflectivity of 95.4% at λ = 368 nm with a bandwidth of 15 nm.