Metal–Organic Chemical Vapor Deposition of n‐AlGaN Grown on Strain‐Relaxed Distributed Bragg Reflector Buffer Layers

The strain relaxation, surface morphology, and reflectivity of AlGaN‐distributed Bragg reflectors (DBRs) grown via metal–organic chemical vapor deposition on AlN/Al 2 O 3 templates are investigated. Strain relaxation begins in a 10‐period Al 0.50 Ga 0.50 N (27 nm)/Al 0.75 Ga 0.25 N (29 nm) DBR, and the degree of strain relaxation (DSR) increases with the number of DBR periods. The 30‐period DBR exhibits a peak reflectivity of 0.82 at 279 nm, with a stopband of 12 nm. The DSR of n ‐Al 0.62 Ga 0.38 N on the 30‐period DBR increases from 70% to 100% as the n ‐Al 0.62 Ga 0.38 N thickness increases from 0.4 to 2.5 μm. Although the surface of a DBR comprises numerous spiral hillocks, n ‐Al 0.62 Ga 0.38 N grown on an AlGaN DBR exhibits a step‐flow growth. A DSR of 100% with threading screw dislocations of 2.0 × 10 8 cm −2 and threading edge dislocations of 1.2 × 10 9 cm −2 is obtained for a 2.5 μm‐thick n ‐Al 0.62 Ga 0.38 N on a 30‐period AlGaN DBR.