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

Thirty-pair Al_0.3 Ga _0.7 N/AlN distributed Bragg reflectors centred at 320nm 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 4mm 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 313nm with a bandwidth of 13nm is obtained.