Molecular beam epitaxy GaAs films on Si, with thicknesses ranging from 0.9–2.0 &mgr;m, were implanted with Si ions at 1.2–2.6 MeV to doses in the range 1015–1016cm−2. Subsequent rapid infrared thermal annealing was carried out at 850 °C for 15 s in a flowing N2atmosphere. Crystalline quality was analyzed by using Rutherfold backscattering/channeling technique and Raman scattering spectrometry. The experimental results show that the recrystallization process greatly depends on the dose and energy of implanted ions. Complete recrystallization with better crystalline quality can be obtained under proper implantation and subsequent annealing. In the improved layer the defect density was much lower than in the as‐grown layer, especially near the interface.