Stopping power of GaAs for swift protons: Dielectric function and optical-data model calculations

The energy-loss-function (ELF) of GaAs determined from optical data has been used to calculate the electronic stopping power (SP) of swift protons in the Born approximation. Along the lines of the Ritchie–Howie scheme, a sum of Drude-type ELFs with finite damping was used to obtain an analytic representation of the experimental data at the optical limit of zero momentum transfer. Consistency was ensured by satisfying both the KK- and f-sum-rule to better than 1%. The mean excitation energy (I-value) of GaAs was calculated at 349 eV which is about 3% higher than the recent estimate of Heredia-Avalos and co-workers S. Heredia-Avalos, J.C. Moreno-Marin, I. Abril, R. Garcia-Molina, Nucl. Inst. Meth. B 230 (2005) 118]. A simple quadratic dispersion relation used to extend the ELF to arbitrary momentum transfers was found adequate for SP calculations above ～300 keV where our results are in good agreement with the available experimental data and other sources in the literature. The limitation of the present scheme at lower proton energies is discussed.