Defect observation of AlInGaP irradiated with 30 keV protons for multi-junction space solar cells

30 keV proton irradiation effects on AlInGaP cells and diodes as a new top cell for high efficiency III-V multijunction (MJ) space solar cells are presented here for the first time. New defects such as two majority-carrier (hole) traps HP1 (E_V+1.57 eV, N_T=3.9×10¹⁴cm^-3), HP2 (E_V+1.19 eV, N_T=2.6×10¹⁴cm^-3) and two minority-carrier (electron) traps EP1, EP2 (E_C-0.71 eV, N_T=2.9×10¹⁵cm^-3) were observed in p-AlInGaP irradiated with a dose of 1 ×10¹²cm^×2 by DLTS measurements. In as-grown samples, the E1 trap appears in both of majority- and minority-carrier DLTS scans, and is attributed to the DX center. The change of remaining factor (V_OC, I_SC, FF, P_max) in the AlInGaP cell with 30 keV proton fluence is evaluated. As the proton fluence increases over 1×10¹⁰cm^-2, the Pmax of the cell decreases rapidly due to the degradation in the fill-factor. At the proton fluence of 1×10¹⁰cm^-2, the short-circuit current rises above the initial value interestingly due to the depletion layer broadening with the majority-carrier removal, and is degraded gradually over 1×10¹⁰cm^-2. On comparing the V_OC, I_SC in the AlInGaP cell (0.6 μm) and InGaP cell (0.6 μm) with proton fluence, AlInGaP shows the higher radiation tolerance than InGaP.