Effects of proton irradiation on n+p InGaP solar cells

3 MeV proton irradiation effects on ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ single junction and ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}/\mathrm{GaAs}$ tandem solar cells have been investigated for the fluence range from ${\text{1×10}}^{11}$ to ${\text{1×10}}^{13}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}.$ The overall radiation degradation of ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}/\mathrm{GaAs}$ tandem cells was higher than ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ single junction cells. It was observed that the spectral response of the GaAs bottom cell degrades more than the InGaP top cell. Proton irradiation decreases the longer wavelength spectral response more significantly than the shorter wavelength in both ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ and ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}/\mathrm{GaAs}$ cells. The difference in the degradation properties of $n^{+}p$ and $p^{+}n$ polarity InGaP solar cells is discussed. The radiation response of a tandem $n^{+}p$ InGaP/GaAs cell is very nearly that which is predicted from the information of these two cells independently. The minority-carrier diffusion length in the base layer was determined from the spectral response data. The minority-carrier diffusion length damage coefficient $K_L$ was analyzed for ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ and GaAs cells. The minority-carrier injection-enhanced annealing of radiation-induced defects in ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ and ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}/\mathrm{GaAs}$ cells were also observed.