We present an experimental investigation of the contribution of secondary fluorescence to the iron signal in proton-induced X-ray emission (PIXE) channeling measurements of Fe-doped GaN layers. A method for the analysis of the PIXE angular scans has been developed, which is necessary for the correct quantification of the lattice site occupation of the Fe atoms in the GaN matrix. This approach should be taken into account any time the lattice location of small amounts of substitutional impurities has to be ...