MBE-grown high-quality (Al, Ga)N/GaN distributed Bragg reflectors for resonant cavity LEDs

High-quality ten-period (Al, Ga)N/GaN Bragg reflectors ( 15% < Al% < 45%), with a target centre wavelength of 510 nm, have been grown by plasma-assist ed molecular beam epitaxy on GaN templates. X-ray diffraction and high-reso lution transmission electron microscopy measurements reveal an excellent cr ystal quality and morphology of the mirrors, and provide an estimate of the structural parameters, including layer thicknesses, Al content and lattice strain. Threading dislocations running through the structure do not affect the interface abruptness or the periodicity. Peak reflectance values up to 58% are achieved, in spite of the rather small number of periods and low A l content. The experimental results are in very good agreement with simulat ed reflectivity spectra. These semitransparent Bragg mirrors are key elemen ts to fabricate backside-emitting resonant-cavity LEDs for plastic optical fibre communications at 510 nm.