Proton Damage Annealing for Use in in Extended Life Solar Arrays

Isochronal and isothermal annealing studies have been performed on low energy (250 keV and 1.5 MeV) proton damage in both silicon and gallium arsenide solar cells. Peculiarities in the fluence dependence of damage in both types of cells are also discussed and modeled in order to augment the annealing analysis. These data are used in conjunction with defect energy level data from other researchers to synthesize a preliminary model for describing the annealing behavior of the proton damage. Important observations from the study are that 1) proton damaged silicon cells can be restored to within 90 to 95% of their initial maximum power in less than five minutes at 400°C, 2) similarly damaged gallium arsenide cells anneal much more slowly than silicon and do not recover as completely at temperatures up to 300°C where thermal degradation was observed in control cells, 3) while all the silicon cells behaved uniformly before and during irradiation, there were wide variations in their annealing responses indicating the apparent presence of an as yet unidentified agent within the material which does not affect initial electrical behavior or radiation damage introduction but radically influences both the degree and the rate of annealing, and 4) the annealing of silicon cells exhibited a dependence on fluence, suggesting that a trade-off exists between frequency of anneals and other economic factors.