Cu-alloyed GaN epilayers were prepared by plasma assisted molecular beam epitaxy in a Ga-rich environment with Cu-to-Ga beam equivalent pressure ratios of 1.2 to 4.8%. Islands enriched with Cu are found on all the GaN epitaxial layers. The islands are composed of a Cu9Ga4 intermetallic phase and GaN with the orientation relationship: [111](Cu9Ga4)//[1 2 10](GaN) and (10 1)(Cu9Ga4)//(0001)(GaN). The formation mechanisms of the islands are discussed in detail. Wavelength dispersive X-ray spectroscopy analyses indicate that the 1.2 and 4.8% samples contain 0.10 +/- 0.02 atom % Cu and 0.04 +/- 0.03 atom % Cu, respectively. Both samples show ferromagnetic behavior with a magnetization of in a range of (2.3-5.1) x 10(3) A/m at saturation. A strategy to suppress the island formation and increase Cu incorporation is accordingly proposed and verified. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3607425] All rights reserved.