Effects of proton radiation on the InGaAs component cells of inverted metamorphic four-junction solar cells

In this study, 5-MeV proton radiation was incident on the InGaAs (1.0 eV) and InGaAs (0.7 eV) component cells of inverted metamorphic four-junction (IMM4J) solar cells. Light current-voltage (LIV), external quantum effi-ciency (EQE), and deep level transient spectroscopy (DLTS) were used to examine the performance degradation and the radiation defects. For the two InGaAs component cells, in case of LIV, open circuit voltage (Voc), short-circuit current (Isc), and the maximum output power (Pmax) decreased linearly with the function of logarithmic change of the proton fluence. Compared to InGaAs (1.0 eV) component cells, for the InGaAs (0.7 eV) component cells, Voc and Pmax decreased considerably and Isc decreased slightly. In EQE, an evident measurement artifact related to the luminescence coupling effect was detected in InGaAs (1.0 eV) before proton radiation, and it disappeared after radiation. This phenomenon was not observed in InGaAs (0.7 eV). In DLTS, a hole trap, H0, was detected at Ev + 0.09 eV in InGaAs (1.0 eV), and three hole traps H1, H2, and H3, were detected at Ev + 0.07 eV, Ev + 0.30 eV, and Ev + 0.45 eV, respectively, in InGaAs (0.7 eV). H0 and H1 were attributed to shallow traps introduced during radiation, and H2 and H3 were the initial defects due to the growth process; moreover, H2 and H3 were determined to be VGa (0/-1) and VGa (-1/-2) or probably VAs (+3/+1).