cancy-interstitial (Frenkel) pair. Surviving vacancies migrate through the lattice and often form electrically active stable defects in conjunction with an impurity or dopant atom. Regardless of whether an atom is displaced as a part of a damage cascade or as an isolated lower energy PKA, most of the initial vacancy-interstitial pairs recombine and no permanent damage results. The interstitial Si atoms do not form electrically active defects. However, the vacancies that escape recombination migrate through the lattice and ultimately form relatively long-lived and immobile defects. Figure 2a is a cartoon illustrating how the initial formation of a Frenkel pair, which is unstable, ultimately results in the formation of a stable defect. These defects have energy levels within the bandgap of the semiconductor. For example, in Si, two vacancies may combine to form a divacancy that is stable up to about 300 °C, or a vacancy and a phosphorous (or oxygen) atom may form an E center (or A center) which is stable up to about 150 °C (or 350 °C), respectively [e.g., Watk64, Walk73 and Kime79]. The vacancy itself is mobile even at liquid nitrogen temperatures, SO it is not practical to attempt to prevent the formation these defects. The process during which the initial vacancy-interstitial pairs evolve into stable room temperature defects results in the so-called "short term annealing effects" in Si devices, and is usually complete within about a second [Srou70, Hein83, Gove84, Mess86]. Figure 2b is a qualitative pictorial showing the time evolution of the number of surviving defects. Note that the stable damage produced in a space environment is very dilute. Longer term room temperature annealing is often observed over a period of IV-54 days or weeks, but it is generally a small effect. For this reason, displacement damage is considered to be a "permanent effect." Vacancy-Interstitial Recombination Number Defects Vacancy Migration Stable Defect Formation Figure 2b Illustration the time evolution of the initial vacancy-interst