des. Similar results were obtained for Si by Mueller et al. who also investigated the defect structure near the end of the recoil track. The term "terminal cluster" has been used to describe the damaged region where the recoil ion loses the last 5-10 keV of energy and has the highest elastic scattering cross section [Muel82]. They found that a single cascade is likely to have 2-3 terminal clusters with a characteristic dimension of 5 nm, connected to each other by a string of dilute displacements. (Note that this size is an upper limit since the calculation does not include the initial vacancy-interstitial recombination.) This result is consistent with transmission electron microscopy measurements [Lars78, Nara81] of 1 MeV, 14 MeV and fission neutron-irradiated Si that have found an average size of 4 nm for the damage. It is clear that the early terminal cluster models based on heavily damaged regions extending for 200 nm [VanL80, and references therein] are not supported by more recent work. Unfortunately, the early cluster models derived support from electron microscopy [Bert68] work that later was shown to be compromised by faulty etching techniques [Nara88]. We also note that electrical measurements on irradiated devices performed in the last decade or SO are also inconsistent with the early cluster models. The interested reader may refer to the literature for details [e.g., Summ87, Peas87, Dale88]. 2.2 Displacement Damage Effects in Materials and Devices The net electrical activity of a given defect with an energy level (E+) in the bandgap is ultimately produced by five basic processes as illustrated in figure 4: (1) the generation of electron-hole pairs, (2) the recombination of electron-hole pairs, (3) carrier trapping, (4) the compensation of donors or acceptors, and (5) the tunneling of carriers. IV-56 Conduction Band DONOR Tunneling Valence Band Generation Recombination Trapping Compensation Figure 4 Schematic of the electrical effects that may occur due to the presence of radiation induced defect level