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High-Reflectivity AlGaN/AlN Distributed Bragg Reflector in Ultraviolet Region

Thirty-pair Al0.3Ga0.7N/AlN distributed Bragg reflectors centred at 320 nm are designed and grown on sapphire substrates by metalorganic chemical vapour deposition. No cracks are observed in the main area of the 2-inch wafer except for about 4 mm margin under an optical microscope. Regular stack of alternating layers is shown by scanning electron microscopy. Clear two-dimensional growth steps and very low surface roughness are shown by atomic force microscopy (AFM). Well-defined periodicity is shown by high resolution x-ray diffraction. High reflectivity of 93% at 313 nm with a bandwidth of 13 nm is obtained.