Abstract：GaInNAs with bandgap 1.0 eV is a promising material for multi-junction solar cell applications. However, the poor quality of GaInNAs grown by metalorganic chemical vapor deposition hinders its device performance. Here to reap the benefits of 1.0-eV sub-cell, we focus on the optimization of annealing temperature and growth ambient of GaInNAs. The GaInNAs sub-cell exhibits a concentration reduction of shallow level defects when it is annealed at 700 $\,^{\circ}\!$C for 20 min. As compared with the growth case using a hydrogen ambient, the N incorporation efficiency of GaInNAs can be enhanced during the growth in an N$_{2}$ ambient. Furthermore, background carbon concentration is observed to reduce in the as-grown GaInNAs epilayer. A GaInNAs sub-cell with 82% peak external quantum efficiency is obtained in a dual-junction GaInNAs/Ge solar cell. Finally, a monolithic AlGaInP/AlGaInAs/GaInAs/GaInNAs/Ge five-junction solar cell is grown for space application. The fabricated device shows a conversion efficiency of 31.09% and a short-circuit current density of 11.81 mA/cm$^{2}$ under 1 sun AM 0 illumination.
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2018, Vol. 35 
