Nitrogen ions (N+, 120 keV) of fluences 1×1014-1×1017 cm-2 have been implanted in liquid encapsulated Czochralski (LEC) grown undoped Semi-Insulating (SI) Gallium Arsenide (GaAs) single crystal substrates. Grazing incidence X-ray diffraction (GIXRD) and Secondary Ion Mass Spectroscopy (SIMS) measurements on control and implanted samples have been carried out and analyzed. For the fluence 1×1015 cm-2, the (311) reflection has been separated into primary and secondary maxima due to implantation induced lattice defects. At a higher fluence (1×1017 cm-2), an additional reflection (111) has been observed. It is due to the structural deformation of GaAs by the implantation process. It is also observed that the FWHM of the (311) reflection peak increased for ion doses up to 1×1016 cm-2 and decreased for the fluence of 1×1017 cm-2. The increase in FWHM is due to strain introduced by the implant. From the SIMS measurements, the atomic distribution of nitrogen (N) has been calculated. © 2002 Elsevier Science B.V. All rights reserved.