Modeling diffusion length damage coefficient in GaAs and InGaP solar cells under electron irradiation

A method is proposed for calculating the diffusion length damage coefficient for minority carriers (KL) in GaAs and InGaP solar cells under electron irradiation using the Shockley–Read–Hall (SRH) model for defect-assisted recombination. In the SRH model, the damage coefficient KL is proportional to the product kσc, where k is the defect introduction rate under particle radiation and σc is the minority carrier capture cross section of the said defects. The introduction rate k is evaluated using the atomic theory for displacement under electron radiation, and the calculation for σc is adapted from Henry and Lang’s high-temperature multiphonon emission formulation. A linear scaling relationship is observed between k,KL and nonionizing energy loss—validated by bibliographic data in the radiation energy range E≈0.7–12 MeV. Our model reproduces the increasing trend in KL with doping, as observed in the literature, while also capturing the anisotropy between the p-type and n-type materials, with the p-type exhibiting greater radiation resistance than its n-type counterpart. The calculated KL is fed into the physical model for solar cell operation to obtain the post-irradiated Isc,Voc,Pmax at a given fluence Φ. The degradation of the electrical quantities is consistent with the measurements recorded in the literature. The findings show that InGaP is more radiation resistant than GaAs. It is demonstrated that calculating k not only aids in determining the degradation of solar cell parameters from first principles, but also in obtaining the empirical function for degradation: a−blog(1+ckΦ), used in fitting the experimental measurements. The limitations and potential scope of improvements in the model are also discussed.