The Al xGa 1−xAs window composition effect on the hardness improvement of a p +–n–n +GaAs solar cell exposed to the electron irradiation

Abstract

Numerical simulation was used to study the Al x Ga 1− x As window composition effect on the current–voltage characteristics of a p +–n–n +GaAs solar cell under AM0 illumination and exposed to 1 MeV electron irradiation. Such solar cells are used in satellites and undergo severe degradation in their performance due to induced structural defects. The irradiation induced defects are modeled as energy levels in the energy gap of GaAs. To predict this effect, the current voltage characteristic and the spectral response are evaluated for different electron irradiation fluences for two types of cells. In the first we use a narrow Al 0.31Ga 0.69As window as a small part of the p + layer while in the second type we use an Al x Ga 1− x As window with a gradual Al mole fraction. The obtained results show that the Al x Ga 1− x As window with a gradual Al mole fraction reduces the degradation of the output parameters of the solar cell and its spectral response by irradiation in particular for the short wavelengths.