High-quality distributed Bragg reflectors based on $AlxGa1−xN/GaN$ multilayers grown by molecular-beam epitaxy

Distributed Bragg reflectors based on $AlxGa1−xN/GaN$ multilayer stacks have been grown by plasma-assisted molecular-beam epitaxy on GaN templates. The nominal Al composition ranged from 30% to 45%, and the layer thicknesses of the ten-period stack were designed for a target wavelength of 510 nm. Transmission electron microscopy data reveal periodic structures where (Al,Ga)N on the GaN interface is sharper than GaN on the (Al,Ga)N one. X-ray diffraction spectra fitted to a dynamic diffraction simulation model yield an estimate of the layer thicknesses, Al%, and lattice strain. Reflectivity values above 50% at 510 nm have been reproducibly achieved, in very good agreement with the results of the matrix-method simulation.