Influence of Zn-Si donor-acceptor pair traps in invert InGaP/GaAs dual-junction solar cell by MOCVD

In In(Ga)P materials, Zn atoms diffuse into the adjacent Si doping layer at high temperatures, forming Zn-Si donor-acceptor pairs which function as non-radiation carrier recombination centers. The traps lead to decreased carrier diffusion length and separation efficiency in the space charge region of InGaP subcell, resulting in degradation of photoelectric conversion efficiency. In this paper, by adopting an InGaP p-i-n junction structure, the invert growth thin film cell was able to reach the same external quantum efficiency performance as the upright InGaP/GaAs dual-junction solar cell. The Zn doping peak was not observed at the Si doping interface layer in the electrochemical capacitance-voltage measurement. A 675 nm peak was observed at 5 and 30 K and absent in 77 K, as was resolved by low-temperature PL measurement. The peak showed a strong correlation with the Zn diffusion into adjacent Si doping InGaP layer. We speculate that the 675 nm peak represented the energy of Zn-Si donor- acceptor pair traps. (C) 2019 The Japan Society of Applied Physics