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

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Abstract
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-assisted molecular beam epitaxy on GaN templates. X-ray diffraction and high-resolution transmission electron microscopy measurements reveal an excellent crystal 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 Al content. The experimental results are in very good agreement with simulated reflectivity spectra. These semitransparent Bragg mirrors are key elements to fabricate backside-emitting resonant-cavity LEDs for plastic optical fibre communications at 510 nm.