Stopping powers of GaAs for 0.32.5 MeV H-1 and He-4 ions

Ion backscattering and foil transmission methods have been used to determine the energy loss of 0.3-2.5 MeV H-1 and He-4 ions in crystalline bulk GaAs and thin foil GaAs grown by molecular beam epitaxy (MBE). The self-supporting GaAs sample foil was produced by floating the MBE-grown GaAs film from an AlAs/GaAs backing by a lift-off process. The stopping powers, corresponding to energy loss of the ions in a nonchannelling direction in the crystal were extracted from the measurements. Ion backscattering and chanelling were employed to study the effect of the crystal structure of the thin foil sample on the stopping powers deduced. Deviations from semi-empirical SRIM calculations (version 96.04) were observed in the case of He-4 ions for which the stopping powers fall clearly below the calculated values. An average deviation of about 5% is found for the energies studied, from below the stopping power maximum at 0.8 to 2.2 MeV. The results obtained by the two independent experimental methods have been compared and discussed.