We report on the growth by molecular-beam epitaxy on 2 in. sapphire substrates of crack-free AlxGa1-xN/GaN distributed Bragg reflectors (DBRs) with high-Al composition (x=0.5). This is achieved by introducing a thick AlN interlayer and strain mediating AlyGa1-yN layer between the substrate and DBR. The relatively larger refractive index ratio between Al0.5Ga0.5N and GaN permits one to obtain a quite large spectral stopband width (49 nm) and a high reflectance value (69%) for only eight mirror periods. (C) 2003 American Institute of Physics.