High quality GaN epilayers were obtained by using a magnesium nitride (Mg_xN_y) inter-layer. X-ray photoelectron spectroscopy (XPS) reveals Mg 2p core-level spectra from the Mg_xN_y inter-layers. The roughness of the Mg_xN_y layers increased with the growth time, though a prolonged processing time resulted in a decrease in the roughness. A high-resolution X-ray diffraction ω-scan rocking curve was used to reveal that the screw dislocation density (TDD) of GaN with an Mg_xN_y inter-layer was reduced and the crystalline quality of the GaN epitaxial layer was enhanced. Furthermore, the luminous efficiency of an LED with the Mg_xN_y layers was increased by 20 % relative to a reference LED.