The 180 keVCa+andAr+ions were homogeneously implanted in GaN at temperature of liquid nitrogen. High resolution x-ray diffraction was used to monitor the change of GaN (0002) peak with the dose ranging from5×1012to1×1016 cm−2. It has been found that with increasing dose a new peak beside the GaN (0002) peak appears, grows up, and gradually shrinks until disappearance with arising of the amorphous peak, accompanied with a shift towards smaller angles. The difference betweenCa+andAr+implantation is discussed. Expansion of GaN crystal lattice due toCa+andAr+implantation accounts for this phenomenon and is confirmed by TEM results. ©1997 American Institute of Physics.