Abstract
Series resistance of Zn-doped p- (GaAl)As/p-GaAs/n-GaAs solar cells fabricated by liquid-phase epitaxy has been theoretically calculated as a function of sheet resistance of p- (GaAl)As and p-GaAs, and also measured experimentally. The series resistance is strongly affected by the p-layer sheet resistance. From the resistivity measurement, it was found that the resistivity of Zn-doped p-Ga0.3Al0.7As is about 10 times higher than that of the Zn-diffused p-GaAs layer. The high resistivity of Zn-doped p-Ga0.3Al0.7As is caused by the deeper acceptor level (Ea=90 meV) than that for Zn-doped p-GaAs (Ea=20 meV). Fabricated p-p-n solar cells have been operated under a concentration of 700 suns. The cells showed nearly constant efficiency at a concentration lower than 100 suns, but the efficiency decreased monotonically above 500 suns because of the series resistance effect. The additional Zn diffusion into p- (GaAl)As has also been performed after the LPE growth in a closed tube by using ZnAs2. The reduction of p- (GaAl)As resistivity was confirmed; the resistivity decreased from 0.4 Ω cm (without additional Zn diffusion) to 0.03 Ω cm (Zn diffusion).
Published Version
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