Numerical simulation of the electron traps effect created by neutron irradiation on $$p^+-n-n^+$$ p + - n - n + GaA
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ORIGINAL PAPER
Numerical simulation of the electron traps effect created by neutron irradiation on pþ n nþ GaAs solar cell performance W Laiadi1*
, Am Meftah2, Af Meftah2 and N Sengouga2
1
Department of Material Science, University of Mohamed Khider Biskra, BP 145 RP, 07000 Biskra, Algeria
2
Laboratory of Metallic and Semiconducting Materials (LMSM), Department of Material Science, University of Mohamed Khider Biskra, BP 145 RP, 07000 Biskra, Algeria Received: 19 December 2019 / Accepted: 04 May 2020
Abstract: Numerical simulation is used in this work to model the effect of 1 MeV neutron irradiation on the performance degradation of a pþ n nþ 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 shortcircuit current density Jsc , the open-circuit voltage Voc , the fill factor FF and the conversion efficiency g) 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 pþ n nþ GaAs solar cell degradation is very apparent at 1014 cm2 neutron irradiation fluence. The deepest electron trap En5, with largest capture cross section, is responsible for the degradation of Jsc and g. 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 pþ GaAs emitter layer from 0.44 to 0.1 lm with keeping a gradual Alx Ga1x As window thickness of 0.09 lm. Keywords: Alx Ga1x As=GaAs solar cell; Neutron irradiation; Defects induced; Degradation
1. Introduction Nuclear radiation in the space environment is one of the principal factors limiting the life span of a space mission. For satellites and space vehicles, the most used energy source is photovoltaic solar cells. Materials that can be used to make solar cells for this purpose have to withstand harsh conditions that include high temperatures and energetic particles. Semiconductors like halide perovskites, and a few materials such as Si, CdS, CdTe and some III–V semiconductors and their alloys (GaAs, InP and GaInP) can meet these conditions [1–8]. GaAs solar cells have been used for space applications since 1982 [9]. Due to their good properties such as high quantum efficiency and good irradiation tolerance, they are the ideal choice for space applications [10, 11]. In comparison with Si space solar
cell, the radiation reliability of GaAs solar cells is over 20% higher and the efficiency of energy conversion
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