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

Abstract

A crack-free GaN∕AlN distributed Bragg reflector (DBR) incorporated with GaN∕AlN 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 GaN∕AlN SL layers and GaN layer were inserted in every five pairs of the 20 pair GaN∕AlN DBR structure to suppress the crack generation. The grown GaN∕AlN DBRs with SL insertion layers showed no observable cracks in the structure and achieved high peak reflectivity of 97% at 399nm with a stop band width of 14nm. 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.