Electron Damage Coefficients in P-Type Silicon

Crucible grown p-type silicon, as used for the base of many commercial solar cells, exhibits a damage coefficient under electron bombardment that appears to involve a double defect in each recombination center. The damage coefficient has been fitted to an empirical formula that accounts for silicon resistivity and for energy of the bombarding particles. To apply this formulation to a practical evaluation of solar cell damage in orbit, two complications were considered. The first is the angular distribution of the space radiation incident on the cell. An experiment showed that electron flux, and not current, determines the extent of the damage. The second is the presence of a transparent coverslide over the cell. By the application of Monte Carlo data for the transmission loss and energy degradation of the electrons, modifications to the damage coefficient can be made to account for coverslide shielding. An exponential attenuation appears adequate to describe these shielding effects. The end product of this study is an analytic formula for the damage coefficient that allows a simple calculation of the damage caused by energetic electrons to n/p silicon solar cells with coverslides.