Crack-free GaN∕AlN distributed Bragg reflectors incorporated with GaN∕AlN superlattices grown by metalorganic chemical vapor deposition

A crack-free $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ distributed Bragg reflector (DBR) incorporated with $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ superlattice (SL) layers was grown on a $c$ -plane sapphire substrate by metalorganic chemical vapor deposition. Three sets of half-wave layers consisting of 5.5 periods of $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ SL layers and GaN layer were inserted in every five pairs of the 20 pair $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ DBR structure to suppress the crack generation. The grown $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ DBRs with SL insertion layers showed no observable cracks in the structure and achieved high peak reflectivity of 97% at $399\mathrm{nm}$ with a stop band width of $14\mathrm{nm}$ . Based on the x-ray analysis, the reduction in the in-plane tensile stress in the DBR structure with insertion of SL layers could be responsible for the suppression of crack formation and achievement of high reflectivity.