Structure, morphology, and optical properties of Gd implanted GaN epitaxial layers were studied for (0001), (11-20), and (11-22) orientations. The GaN layers grown by MOVPE on sapphire were subsequently implanted with 200 keV Gd+ ions using fluences of 5 x 10(15) and 5 x 10(16) cm(-2). Dopant depth profiling was accomplished by Rutherford Back-Scattering spectrometry (RBS). Structural and optical changes during subsequent annealing were characterized by RBS, Raman spectroscopy, and photoluminescence measurements. Post-implantation annealing induced a structural reorganization of GaN structure in the buried layer depending on the introduced disorder level, i.e. depending on the implantation fluence and on crystallographic orientation. The defect density depth distribution was evaluated by RBS. The surface morphology and optical properties depend on particular crystallographic orientation. (C) 2017 Elsevier B.V. All rights reserved.