Radiation Effects Of Space Charged Particales And Methods Of Predicting Degradation Of Performance In Orbit For GaAs Solar Cells

The degradation and damage mechanisms caused by irradiation of space charged particles are investigated for the domestic GaAs/Ge and GaInP/GaAs/Ge solar cells, based on equivalent ground simulation experiments. The methods of evaluating performance in orbit for the GaAs/Ge single-junction solar cells are simplified and improved, and are further applied to the GaInP/GaAs/Ge triple-junction solar cells. The performance of the GaAs/Ge and GaInP/GaAs/Ge solar cells in the geostationary orbit is evaluated.Experimental results show that under exposure of protons with various energies, the degradation in electric characteristics of the GaAs/Ge single-junction solar cells can be related to the damage in the emitter, the base and the space charge regions, respectively. The 70keV protons primarily lead to the damage in the space charge region and an obvious degradation in the open voltage. The 40keV protons mainly result in the damage in the emitter and a considerable degradation in short circuit current. Under the >100keV protons exposure, the degradation of electric properties gradually decrease with increasing proton energy. Compared at a given fluence of electrons, the electric characteristics of the GaAs/Ge solar cells increase with increasing electron energy. The exposure sequence of 1MeV electrons and 170keV protons does not influence irradiation damage to the GaAs/Ge cells. DLTS analysis shows that the irradiation-induced defects caused by <200keV protons in the GaAs/Ge solar cells are mainly the Ec-0.31eV and Ec-0.47eV, and their concentration decreases with increasing proton energy. On the basis of the irradiation-induced damage effects, two physical-mathematic models on the degradation in electric characteristics of the GaAs/Ge single-junction cells are set up, which are separately responsible for the short circuit current and the open circuit voltage.Under <200keV proton exposure, the degradation in electric characteristics of the GaInP/GaAs/Ge triple-junction cells has a close relationship with proton energy. Compared at a given fluence, the 170keV proton exposure leads to the largest degradation magnitude of the open circuit voltage, short circuit current and maximum power. In contrast, the degradation magnitude in the electric characteristics caused by the 40, 100 and 130keV protons is lower. Under the irradiation of protons with 4MeV and 10MeV, the degradation magnitude in electric characteristics decreases with increasing proton energy. At a given fluence, the degradation magnitude in electric characteristics increases with increasing electron energy. ODLTS analysis shows that the <200keV protons can introduce the deep-energy levels of Ec-0.26, Ev+0.18eV and Ev+0.42eV in the GaInP sub-cell, and those of Ec-0.015eV, Ec-0.15eV and Ev+0.33eV in the GaAs sub-cell.The effect of <200keV proton flux on the radiation damage of the GaAs/Ge single-junction cells is studied, on both the experimental and theoretical analyses. It is shown that the proton flux ranged from 6×109 to 1.2×1011cm-2s-1 does not have effects on the radiation damage of the GaAs/Ge cells. This can provide a basis of accelerating ground simulation for space charged particle irradiation. Both degradation curves and the dynamic equation for the electric characteristics of the domestic GaInP/GaAs/Ge cells are established through experiments. Also, the relative damage coefficients to convert fluences for particles with different energies are given for the domestic GaAs/Ge and GaInP/GaAs/Ge cells. The equivalent fluences for orbits are calculated in terms of the energy spectra of space charged particles that penetrate through the coverglass. As a result, the calculation for the equivalent fluence method can be simplified.On the basis of radiation-induced damage effects caused by protons with lower energies, the relative equivalent coefficients to convert the displacement damage doses for the <70keV protons and >70keV protons are given for the domestic GaAs/Ge cells. Furthermore, the improved displacement damage dose method is applied to evaluating the GaInP/GaAs/Ge triple-junction cells. The degradation behaviors in the geostationary orbit of the domestic GaAs/Ge and GaInP/GaAs/Ge cells with a coverglass plate of 120μm in thickness are predicted, using both the improved equivalent fluence method and displacement damage dose method. The predicting results are in good agreement for the two evaluating methods, illustrating that the improved predicting methods are applicable in practice.