Properties of an AlGaN/AlN distributed-Bragg-reflector structure

An AlGaN/AlN distributed-Bragg-reflector (DBR) structure with a high Al content was grown by using plasma-assisted molecular beam epitaxy (PA-MBE). The properties of the sample were characterized by using the transmission electron microscopy, high-resolution X-ray diffraction, atomic force microscopy, and reflectivity spectrum measurements. The reciprocal space mapping analysis indicated that the strain in the AlGaN layers was partially relaxed. The morphology of the DBR exhibited a surface covered by grains (average size of about 130 nm), and the surface roughness was about 2 nm. The spectral measurements showed that the DBR structure presented a peak reflectivity of 68.8% at the center wavelength of 247 nm, which indicated that this DBR structure could work in the deep solar-blind UV region with acceptable reflectivity. However, the optical properties of the DBR structure were deteriorated by the fluctuation of the Al composition, non-uniformity of the layer thickness, the blurry, rough interface in the DBR structure, and so on.