The use of nonionizing energy loss (NIEL) in predicting the effect of gamma, electron and proton irradiations on Si, GaAs and InP devices is discussed. The NIEL for electrons and protons has been calculated from the displacement threshold to 200 MeV. Convoluting the electron NIEL with the "slowed down" Compton secondary electron spectrum gives an effective NIEL for C o a gammas, enabling gamma-induced displacement damage to be correlated with particle results. The fluences of 1 MeV electrons equivalent to irradiation with 1 Mrad(Si) for Si. GaAs and InP are given. Analytic proton NIEL calculations and results derived from the Monte Carlo code TRIM agree exactly so long as straggling is not significant. The NIEL calculations are compared with experimental proton and electron damage coefficients using solar cells as examples. A linear relationship is found between the NIEL and proton damage coefficients for Si, GaAs and InP devices. For electrons, there appears to be a linear dependence for n-Si and n-GaAs, but for p-Si there is a quadratic relationship which decreases the damage coefficient at 1 MeV by a factor of-10 below the value for n-Si. The present results greatly extend the range of environments for which damage calculations based on NIEL can be applied. The NIEL results are presented in tabular form for ease of calculation. * The threshold energies used were 21 and 12.9 eV for Si; 10 eV for Ga and As; 6.7 eV for In and 8.7 eV for P.

The method for predicting solar cell degradation in space radiation environments developed recently at the US Naval Research Laboratory (NRL) is compared in detail with the earlier method developed at the US Jet Propulsion Laboratory (JPL). Although both methods are similar, the key difference is that in the NRL approach, the energy dependence of the damage coef®cients is determined from a calculation of the nonionizing energy loss (NIEL) and requires relatively few experimental measurements, whereas in the JPL method the damage coef®cients have to be determined using an extensive set of experimental measurements. The end result of the NRL approach is a determination of a single characteristic degradation curve for a cell technology, which is measured against displacement damage dose rather than¯uence. The end-of-life (EOL) cell performance for a particular mission can be read from the characteristic curve once the displacement damage dose for the mission has been determined. In the JPL method, the end result is a determination of the equivalent 1 MeV electron¯uence, which would cause the same level of degradation as the actual space environment. The two approaches give similar results for GaAs/ Ge solar cells, for which a large database exists. Because the NRL method requires far less experimental data than the JPL method, it is more readily applied to emerging cell technologies for which extensive radiation measurements are not available. The NRL approach is being incorporated into a code named SAVANT by researchers at NASA Glenn Research Center. The predictions of SAVANT are shown to agree closely with actual space data for GaAs/Ge and CuInSe 2 cells¯own on the Equator-S mission.

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