Figure 2.2-7. Normalized Solar Cell Maximum Power Versus 1-Mev Electron Fluence coefficient and short lifetimes which are characteristic of direct bandgap materials. For example, for GaAs cells any lattice damage created more than approximately 6 pm below the surface has no effect on the output power of the cell. However, low-energy particles with ranges of only several microns can degrade the direct bandgap cells. The GaAs cells have more than an order of magnitude more resistance to high-energy electrons and protons compared to Si cells, but are susceptible to low-energy protons because of the heavy damage created in the first micron below the surface. A thin coverglass, or similar material, will filter out the low-energy particles and should make GaAs cells more resistant than Si cells at all particle energies^.