Proton radiation hardness of GaInAsP alloys for space solar cell applications

Recent technology development in space mission design has raised a demand for space solar cells with a higher level of radiation tolerance as compared with state-of-the-art, commercially available products. Therefore, new material systems are being investigated. Recently, we highlighted the superior radiation tolerance of GaInAsP solar cells to 1 MeV electron irradiation as compared with standard GaAs solar cells. A high InP fraction within this semiconductor compound was found to foster the regeneration rate of electron-induced defects when the solar cells were annealed at 60°C under AM0 illumination, which are typical space-operating conditions. In light of considering this material system in future radiation-hard designs, the degradation of GaInAsP solar cells subjected to proton irradiation also needs to be investigated. Here, we report on the degradation and regeneration of GaInAsP solar cells lattice-matched to InP substrates after 1 MeV proton irradiation. A detailed description of the radiation damage is achieved by solar cell numerical modeling combined with deep-level transient spectroscopy analysis. The irradiation-induced defects are quantified, and their evolution during annealing is monitored. The results are compared with the degradation data of similar solar cells obtained after 1 MeV electron irradiation. A slower regeneration rate of the proton-induced defects is found in comparison with the electron-induced defects. This difference is ultimately attributed to a different topology of the radiation damage caused by proton irradiation.