Suppression of crack generation in GaN/AlGaN distributed Bragg reflector on sapphire by the insertion of GaN/AlGaN superlattice grown by metal-organic chemical vapor deposition

GaN/AlGaN distributed Bragg reflectors (DBRs) have been grown on sapphire by metal-organic chemical vapor deposition. A GaN/AlGaN superlattice (SL) was introduced prior to the growth of the DBR to suppress crack generation. By introducing the SL. GaN layers in the DBR were highly compressed and the in-plane lattice constants were close to those of AlGaN layers in the DBR. For the 30 pairs of GaN/Al_0.41Ga_0.59N DBRs, the reflectivity was improved from 93% to 98% by the introduction of the 100 periods of GaN/AlGaN SL, and the generation of cracks was effectively suppressed.