s the average energy required to generate one electron and one hole in SiO2 via high-energy interactions (an experimental value). Note that, the experimental uncertainty being of the order of 1 eV, some authors use go=8.2 10 12 coming from w=17 eV. However, SiO2 seems to be an exception as compared to Si, GaAs, C, etc., because a certain amount of electron and holes recombine, and this recombination depends essentially on the electric field applied. This "mutual recombination" of the generated carriers is the first part of a series of processes, well separated in time, whereas charge trapping is the last picture. In this series of successive interactions and physics that takes place from the very early moment of energy deposition, let us come back to this early events when the tracks take form. III-17 CLOUD OF ELECTRONS AND HOLES 10-keV X-RAYS ELECTRON TRACK 700-keV PROTONS POSITIVE BIAS 2-MeV a PARTICLES ELECTRIC FIELD (MV/cm) Figure 13. Fraction of unrecombined pairs versus the applied electric field Figure 12. Separation of electron and holes. for various incident radiations [McGa-80], [Oldh-83]. According to the particles that interact with the oxide, the density of ionization is more or less important and two borderline cases are considered: The recombination of one particle of the pair undertaken with the parent particle. It is the case for electrons or incident photons that give a weak density of ionization. The recombination undertaken randomly with a not-correlated particle in the ionized column. It is the case for ionization due to heavy particles. The fraction of pairs that overcome this initial recombination and separate depends therefore on energy and the type of the incident particle and also on the electrical field present in the insulator that favors this separation. This fraction has been characterized by several independent workers working on scaled technologies since the mid 70' S: [Ausm- 75] initiated with 105 nm oxide and 4 keV electrons, [Srou-77b] compared the yield at 77K and 300K, [Hugh-7