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In this study we overcame several critical growth issues related to epitaxy in AlGaN deep-ultraviolet light-emitting diodes. Irregular-shaped pits with dislocation clusters were observed in micron-thick layers of AlGaN on AlN. The strain-induced morphology and defects were suppressed after the insertion of superlattice transition layers between the AlGaN and AlN layers. The defect luminescence in the active region was governed by radiative recombination through the oxygen shallow donors and deep acceptors related to III-vacancies. After optimization of the growth conditions and a decrease in growth interruption, the intensity of the parasitic blue-band emission was suppressed by up to 95%. Energy dispersive spectroscopy suggests that the desorption of gallium from the surface is the major source of the III-vacancies. Keywords: Defects, Line defects, Point defects, Surface structures, Metalorganic vapor phase epitaxy, Light-emitting diodes