Fe-containing Bi 2 Se 3 Topological Insulators (TI) thin films have been grown to investigate the intricate interplay between topological order and the incorporation of ferromagnetic atoms. Here we present the quantitative characterisation of the Bi 2 Se 3 thin films with up to 16 at% Fe incorporated during the growth process on GaAs (111) substrate by Molecular Beam Epitaxy. We report the elemental composition and depth profiles of the Bi 2 Se 3 :Fe films obtained using Rutherford Backscattering Spectrometry (RBS) and their formed crystalline phase obtained by X-Ray Diffraction (XRD). Resistance of the TI to beam-induced damage was investigated by channelling RBS. Using the elemental composition from RBS and the thickness from XRD measurements the Fe-free film density was deduced. For Fe-containing samples, the diffraction reveals the formation of two distinct crystalline phases, as well as their intergrowth pattern, in which the basal planes of Bi 2 Se 3 coexist with an additional Fe-Se phase. This intergrown composite, with chemical compatibility of the Fe-Se phase with the crystalline Bi 2 Se 3 structure, preserves the intrinsic topological surface states of the TI component despite the inhomogeneous distribution of the constituent phases. RBS analysis gives the stoichiometry of the Bi 2 Se 3 , and Bi 2 Se 3 :Fe samples (estimated between 0-16 atom% Fe) and gives insights into the composition of FeSe x phases present.