Numerical simulation of the electron traps effect created by neutron irradiation on 𝑝+−𝑛−𝑛+GaAs solar cell performance

Numerical simulation is used in this work to model the effect of 1 MeV neutron irradiation on the performance degradation of a 𝑝+−𝑛−𝑛+ GaAs solar cell. The effect is predicted by the calculation of the current–voltage characteristics under AM0 illumination for a constant dose of neutron irradiation. The solar cell output parameters (the short-circuit current density 𝐽sc, the open-circuit voltage 𝑉oc, the fill factor FF and the conversion efficiency 𝜂) are extracted from these characteristics. The neutron irradiation induced five electron traps En1, En2, En3, En4 and En5 in the energy gap either as recombination centers or traps. The degradation by the induced traps is widely attributed to the first type of defects. Simulating the effect of each trap level separately helps to find out which of them is responsible for the degradation of a particular output parameter. The simulation results have shown that the 𝑝+−𝑛−𝑛+ GaAs solar cell degradation is very apparent at 1014 cm−2 neutron irradiation fluence. The deepest electron trap En5, with largest capture cross section, is responsible for the degradation of 𝐽sc and 𝜂. The other electron traps En1, En2, En3 and En4 have a no significant effect on the solar cell output parameters, particularly on the open-circuit voltage 𝑉oc. Finally, the solar cell resistivity to the neutron irradiation can be improved by decreasing the thickness of 𝑝+GaAs emitter layer from 0.44 to 0.1 μm with keeping a gradual Al𝑥 Ga1−𝑥As window thickness of 0.09 μm. (author)