Displacement damage in GaAs structures

High-energy knock-on atoms produced by incident protons are much more important in determining the total nonionizing energy deposited in GaAs than in Si, due to the relative size of the Lindhard correction for partitioning the recoil energy. High-energy recoils are mainly produced by inelastic nuclear interactions between the incident protons and the target atoms. A review of previous calculations indicates that both the fast cascade and the evaporation phases of the elastic interaction contribute to the average energy of the recoiling ion. New calculations are presented for the energy dependence of the nonionizing energy deposited in GaAs as a result of inelastic interaction with protons over the energy range 10-1000 MeV. These calculations are combined with the previously determined contribution from elastic interactions to obtain the energy dependence of the total nonionizing energy deposited in GaAs by protons. The calculation is compared with both new and earlier experimental data for ion-implanted GaAs resistors irradiated with protons over the energy range 40-188 MeV, in order to form a basis whereby proton displacement effects in GaAs structures can be predicted. It is shown that results obtained for 10 MeV protons, for example, can be used to predict results to be expected at much higher energies     

Probability of large solar proton events and their effect on the efficiency of GaAs solar cells

Using a recently updated database that includes the last four complete solar cycles, the probability of occurrence of large solar proton events has been analyzed for time periods of up to seven active solar years using extreme value statistics. Then an approach is presented for evaluating solar cell efficiency degradation caused by the large event. These results enable spacecraft designers to evaluate precisely the risk of exposure of solar arrays to large solar proton events over the course of a mission. As an example, the efficiency degradation of n/p GaAs/Ge solar cells caused by an event with a >10-MeV fluence of 1×10¹⁰cm⁻² is shown. This is compared to the degradation resulting from all events in the last solar cycle, and to the electron environment in geostationary orbit over the same period of time. Copyright © 1998 John Wiley & Sons, Ltd.     

Gamma induced dose fluctuations in a charge injection device

Spatial fluctuations in absorbed dose became important as device dimensions are scaled downward and the number of elements on a single chip increased. Furthermore, the extreme events in the distribution could determine the satisfactory operation of the array. The large sample size available in a charge injection device (CID) has made it possible, for the first time, to compare experimental results for gamma-induced dose fluctuations with theoretical calculations of extreme value distributions. The agreement between theory and experiment is excellent. In order to predict correctly the variance in the dose distribution from the basic model for solid-state imagers, it is found to be necessary in the case of a CID to include a term for carrier diffusion     

Modeling solar cell degradation in space: A comparison of the NRL displacement damage dose and the JPL equivalent fluence approaches†

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 coefficients is determined from a calculation of the nonionizing energy loss (NIEL) and requires relatively few experimental measurements, whereas in the JPL method the damage coefficients 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 fluence. 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 fluence, 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 CuInSe₂ cells flown on the Equator‐S mission. Published in 2001 by John Wiley & Sons, Ltd.