Abstract : A high energy electron beam propagating at glancing angles along a mono crystal axis experience a collective scattering from many crystal atoms and may hence, be channeled; it performs an oscillating trajectory and emits a large number of photons. This property is used to obtain an intense beam of photons which generate a large number of e(+)e(-) pairs in an amorphous target. The radiation in crystals is handled by dedicated programs as FOT while the interaction between charged particles and amorphous material is well described in Monte Carlo codes such as Geant4 or EGS. Thus a Monte Carlo code associating the crystal program FOT with Geant4 has been worked out and a presentation is given for this new program named G4Fot. An application to the future positron baseline of the Compact Linear Collider (CLIC) using a tungsten crystal oriented on its < 111 > axis and an amorphous material, the so called hybrid source is also presented.