Raman spectroscopy has been used to study the lattice properties of plasma-assisted molecular beam epitaxy grown GaN:Mn layers (0-18% Mn). Raman spectra corresponding to the intrinsic GaN layers demonstrate three Raman active excitations at 144, 570 and 729.2 cm(-1), identified as E-2(L), E-2(H) and A(1)(LO) respectively. The Mn-doped GaN layers exhibit additional excitations attributed to defect-activated Raman scattering and Mn-m-N (m = 1-4) related frequency modes in the vicinity of E-2(H) mode. Subsequently, detailed X-ray diffraction measurements have revealed the coexistence of cubic phases in the predominantly hexagonal GaN lattice. (c) 2006 Elsevier B.V. All rights reserved.