A study of the collection efficiency of electron-hole pairs in amorphous silicon-carbon based p-i-n structures under keV electron irradiation is presented. a-Si:C:H films have been prepared by a conventional RF plasma deposition technique. A scanning electron microscope in the spot-mode regime was used for electron irradiation of our structures. The current-voltage characteristics and spectral dependence of the short-circuit current were measured. A numerical current transport model was used for simulation and the energy of the electron-hole pair creation Eeh = 7-8eV was determined.