50 keV hydrogen ion implantation has been carried out on undoped semi-insulating (100) gallium arsenide single crystal for various ion doses at room temperature. The defects introduced due to implantation were studied using Raman technique. Two peak were fitted for A1(LO) Lorentizian mode. Two peaks were due to strained and unstrained layers respectively. FWHM increased and the peak position decreased with respect to increase in hydrogen dose, all these effects are due to implantation induced lattice disorder. For higher 1016 the strained peak was not observed. This strain introduced due to chemo-mechanical polising is removed in higher doses.