Radiation degradation prediction for InGaP solar cells by using appropriate estimation method for displacement threshold energy

InGaP solar cells are not predicted to be susceptible to displacement damage by irradiation with electrons at energies lower than 100 keV from non-ionizing energy loss (NIEL) calculations. However, it is recently observed that InGaP solar cells are shown to degrade by irradiation with 60 keV electrons. This degradation is considered to be caused by radiation defects but is not clear. In this study, the kind of the defects generated by electrons at energies lower than 100 keV is found by deep-level transient spectroscopy (DLTS). The result of DLTS indicates that the prediction of primary knock-on atoms by using the radiation damage model is different from the experiment. In order to suggest the generation mechanism of radiation defects, we propose a new displacement threshold energy (E_d) by using a new technique in which NIEL and the introduction rate of radiation defects are combined. The degradation prediction by using estimated E_d is found to agree well with the degradation of electric power of InGaP solar cells irradiated by low-energy electrons. From the theory of radiation defects, we propose a new obtaining process of suitable degradation prediction by the displacement damage dose method.